docs: Add structure and initial content

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

docs/index.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+Build system documentation
+##########################
+
+.. toctree::
+   :maxdepth: 1
+      
+   openharmony-quick-build
+   yocto-build-system/index
+   repo-workspace
+   build-flavours/index
+   ohos-build/index
+   demos/index
+   hardware-support/index

docs/ohos-build/index.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+Build Configuration
+###################
+
+The build system recipes provide various functionalities that expose knobs and
+primitives.
+
+.. toctree::
+   :maxdepth: 1
+   
+   visual-customizations

docs/ohos-build/visual-customizations.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+Build System Visual Customizations
+##################################
+
+.. contents:: 
+   :depth: 2
+
+Weston dynamic configuration
+****************************
+
+The build exposes mechanism to tweak weston configuration through build
+variables. These variables can be provided as part of any configuration (eg.
+*local.conf*, *distro.conf*).
+
+The mechanism is enabled by setting ``WESTON_DYNAMIC_INI`` to ``1``. Any of the
+following variables will be ignored if this variable is not set to ``1``. The
+configuration file path can also be set via a variable: ``WESTON_INI_PATH``.
+The default value of ``WESTON_INI_PATH`` should be fine for most of the cases.
+
+Additional variable to be used in conjuction with ``WESTON_DYNAMIC_INI``:
+
+* ``WESTON_INI_NO_TOOLBAR`` - remove the shell panel when set to ``1``
+* Configuration for shell background
+  * ``WESTON_INI_BACKGROUND_IMAGE`` - sets shell.background-image accordingly
+  * ``WESTON_INI_BACKGROUND_COLOR`` - sets shell.background-color accordingly
+  * ``WESTON_INI_BACKGROUND_TYPE`` - sets shell.background-type accordingly
+
+Epiphany support for Application mode
+*************************************
+
+Epiphany is one of the browsers supported by the build meta-data. It provides a
+webkitgtk-based browser.
+
+The build exposes the ability to run the browser as a system service in
+application mode. This can be easily configurable and extended via the build
+metadata and variables.
+
+Available variables:
+
+* ``EPIPHANY_APP`` - the application name
+* ``EPIPHANY_URL`` - the URL to be used when browser starts
+* ``EPIPHANY_RDEPENDS`` - additional dependencies needed at runtime
+* ``EPIPHANY_SERVICE_ENABLED`` - when set to ``1``, build system will enable
+  the systemd service for starting at boot
+
+The build system provides support for using this mechanism with *HomeAssistant*. See this support as an example for how to implement a custom application mode for Epiphany.

docs/openharmony-quick-build.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+OpenHarmony - Quick Build
+#########################
+
+This section will guide you to building your first OpenHarmony image targeting
+a supported reference hardware. It will also provide the steps for flashing and
+booting such an image.
+
+The steps below will focus on a Qemu-based target. If you want to get a feeling
+of OpenHarmony on a real hardware, checkout the :ref:`Avenger96 support page
+<SupportedBoardAvenger96>`.
+
+.. contents:: 
+    :depth: 2
+
+Prerequisites
+*************
+
+Have a **Ubuntu 20.04 LTS** host with all the required host packages.
+
+.. code-block:: console
+
+    $ sudo apt-get install gawk wget git diffstat unzip texinfo gcc-multilib \
+    build-essential chrpath socat cpio python3 python3-pip python3-pexpect \
+    xz-utils debianutils iputils-ping python3-git python3-jinja2 libegl1-mesa libsdl1.2-dev \
+    pylint3 xterm 
+
+
+Clone build system repositories
+*******************************
+
+Install Google git repo tool:
+
+.. code-block:: console
+
+    $ sudo add-apt-repository ppa:openharmony/tools
+    $ sudo apt-get update
+    $ sudo apt-get install git-repo
+
+Initialize a repo workspace and clone all required repositories:
+
+.. code-block:: console
+
+    $ mkdir ohos; cd ohos
+    $ repo init -u https://git.ostc-eu.org/OSTC/OHOS/manifest.git -b develop
+    $ repo sync --no-clone-bundle
+
+Build the openharmony-image-base image
+**************************************
+
+The following steps will build a ``openharmony-image-base``. The process will
+build all its components, including the toolchain, from source.
+
+First of all change directory into the one where the build repositories were
+cloned using the repo tool. See above.
+
+Initialize the build directory and run a build:
+
+.. code-block:: console
+
+    $ TEMPLATECONF=../sources/meta-ohos/flavours/linux . ./sources/poky/oe-init-build-env build-ohos-linux
+    $ MACHINE=qemux86-64 bitbake openharmony-image-base
+
+Booting a Qemu X86-64 target with a OpenHarmony image
+*****************************************************
+
+Once the build is done, you can run a Qemu X86-64 instance as it follows:
+
+Once the image is done, you can run the Qemu usin the provided script wrapper:
+
+.. code-block:: console
+
+      $ MACHINE=qemux86-64 runqemu
+
+If the host has a VT-capable CPU, you can pass the ``kvm`` argument for better
+performance. Check ``runqemu``'s help message for all available arguments.

docs/repo-workspace.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+.. _RepoWorkspace:
+
+Repo Workspace
+##############
+
+OpenHarmony uses `repo <https://android.googlesource.com/tools/repo>`_ to
+provide full workspace setup that includes all the repositories needed for
+building OpenHarmony and developing on top.
+
+.. contents:: 
+    :depth: 2
+
+The Repo Tool
+*************
+
+OpenHarmony provides a patched version of the repo tool published as a
+`launchpad PPA <https://launchpad.net/~openharmony/+archive/ubuntu/tools>`_.
+The patches are also available in the tool's `source repository <https://git.ostc-eu.org/OSTC/packaging/git-repo>`_.
+
+Install this tool by following the next steps:
+
+.. code-block:: console
+
+   $ sudo add-apt-repository ppa:openharmony/tools
+   $ sudo apt-get update
+   $ sudo apt-get install git-repo
+
+The Manifests
+*************
+
+The `manifest repository <https://git.ostc-eu.org/OSTC/OHOS/manifest>`_
+provides the manifests available for configuring a workspace. The project provides two kinds of manifests:
+
+* develop manifests (where some projects are following a branch)
+* default manifests (where all projects are pinned to specific revisions)
+
+Setting up the Workspace
+************************
+
+Once the repo tool is installed, you can initialize and populate the workspace.
+This will bring in all the needed sources for building Openharmony:
+
+.. code-block:: console
+
+   $ mkdir ohos; cd ohos
+   $ repo init -u https://git.ostc-eu.org/OSTC/OHOS/manifest.git -b stable
+   $ repo sync --no-clone-bundle
+
+You can checkout latest development source code by using *develop* branch
+instead of *stable* as part of the above repo init command.
+
+Workspace structure
+*******************
+
+A fully set workspace, will provide a structure similar to:
+
+.. code-block:: none
+
+   ./ohos/
+   └── sources
+       ├── meta-freertos
+       ├── meta-ohos
+       ├── meta-openembedded
+       ├── meta-zephyr
+       ├── <various yocto layers>
+       └── poky
+
+The *sources* directory will include ``poky`` and  all the build system layers
+that are part of the build process. Any new layers will be included under this
+directory.
+
+It is recommended to use the root of the workspace for the build directories
+using ``build`` as directory name prefix.

docs/yocto-build-system/assets/meta-ohos-arch.png.license

+SPDX-FileCopyrightText: Huawei Inc.
+
+SPDX-License-Identifier: CC-BY-4.0
\ No newline at end of file

docs/yocto-build-system/assets/ohos-build-arch.puml

+' SPDX-FileCopyrightText: Huawei Inc.
+'
+' SPDX-License-Identifier: CC-BY-4.0
+
+@startuml meta-ohos-arch
+!include https://raw.githubusercontent.com/plantuml-stdlib/C4-PlantUML/master/C4_Container.puml
+
+Person(dev, "Developer", "Anyone willing to build the OHOS based image")
+System(meta_ohos, "meta-ohos", "OpenHarmony OS umbrella bitbake meta-layer")
+Boundary(poky, "poky") {
+    System_Ext(bitbake, "bitbake", "build process orchestrator")
+    System_Ext(linux_yocto, "linux-yocto", "Yocto Project LTS linux kernel")
+    System_Ext(meta_external_toolchain, "meta-external-toolchain", "Yocto Project LTS GNU GCC and LLVM toolchains")
+}
+System_Ext(meta_zephyr, "meta-zephyr", "ZephyrOS meta-layer")
+System_Ext(meta_freertos, "meta-freertos", "FreeRTOS meta-layer")
+System_Ext(meta_freertos, "meta-freertos", "FreeRTOS meta-layer")
+System_Ext(linux_yocto, "linux-yocto", "Yocto Project LTS linux kernel")
+System_Ext(meta_external_toolchain, "meta-external-toolchain", "Yocto Project LTS GNU GCC and LLVM toolchains")
+
+Rel(dev, bitbake, "selects configuration, initiates the build, deploys image to the target")
+Rel(bitbake, meta_ohos, "incorporates meta-layers relevant for selected kernel / configuration")
+Rel(bitbake, linux_yocto, "incorporates Yocto Project LTS linux kernel reference")
+Rel(bitbake, meta_external_toolchain, "incorporates Yocto Project LTS toolchains")
+Rel(bitbake, meta_zephyr, "incorporates for OHOS on Zephyr build")
+Rel(bitbake, meta_freertos, "incorporates for OHOS on FreeRTOS build")
+
+@enduml

docs/yocto-build-system/index.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+OpenHarmony, a Yocto-based Build System
+#######################################
+
+OpenHarmony build system, the foundation of the build infrastructure, is based
+on `Poky, the Yocto Project open source reference embedded distribution <https://www.yoctoproject.org/software-overview/>`_.
+This section details both generic and OpenHarmony specific aspects of the build system.
+
+.. toctree::
+   :maxdepth: 1
+   
+   yocto-project
+   ohos-build-arch

docs/yocto-build-system/ohos-build-arch.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+OpenHarmony Build Architecture
+##############################
+
+``meta-ohos`` architecture is documented using `c4 model <https://c4model.com/>`_.
+
+.. contents:: 
+    :depth: 2
+
+Overview
+********
+
+OpenHarmony build infrastructure designed to run atop variety of OS kernels
+ranging from RTOSs to Linux.
+
+``meta-ohos`` is a *umbrella* of meta layers containing build meta-data
+required for compiling OpenHarmony images. The architecture supports plugging
+various kernels.
+
+.. image:: assets/meta-ohos-arch.png

docs/yocto-build-system/yocto-project.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+Poky/Yocto Project
+##################
+
+OpenHarmony aims to use standard opensource tools to create a build environment
+that is both familiar to users in the domain but also flexible enough for the
+requirements of the project. With this in mind, the project build
+infrastructure is based on the OpenEmbedded build system, more specifically
+`Poky, the Yocto Project open source reference embedded distribution <https://www.yoctoproject.org/software-overview/>`_.
+
+.. contents:: 
+    :depth: 3
+
+Build System Concepts
+*********************
+
+The build system uses build instruction files that in the language of the
+system are called ``recipes`` and ``layers``.
+
+Layers are one of the fundamental models of the build system. It enables both
+collaboration and customization by defining scoped meta-data. These layers
+become a collection of build instruction files that have a defined scope. For
+example, there are BSP (board support package) layers that enable board support
+in the build system.
+
+See `terms  for reference <https://www.yoctoproject.org/software-overview/>`_
+for more information.
+
+OpenHarmony Build Layers
+------------------------
+
+OpenHarmony bases its build setup on Poky, the Yocto Project open source
+reference embedded distribution. The main hub of layers, is `meta-ohos <https://git.ostc-eu.org/OSTC/meta-ohos/>`_,
+a collection of layers with different scopes for defining the project's
+requirements and capabilities.
+
+For example, ``meta-ohos-core`` provides build recipes for defining the core
+policies of the build infrastructure (`distribution` configuration, images,
+core packages customization, etc.).
+
+Another example is ``meta-ohos-staging``, a layer that provides temporary fixes
+and support for changes that are aimed upstream but have this place until
+upstream catches up.
+
+For more details of each provided layer of ``meta-ohos``, see the relevant
+``README.md`` file at the root of the layer,
+
+Besides the ``meta-ohos`` collection of layers, the project is also the home
+to a set of other build system layers. Explore them all in our project `GitLab <https://git.ostc-eu.org/OSTC/OHOS>`_
+instance.
+
+Aditional Documentation
+***********************
+
+`Yocto Project <https://www.yoctoproject.org>`_ provides extensive
+documentation on various aspects of the build system. For the general usage of the build system, it's components, architecture and capabilities consult the following resources:
+
+- `Yocto Project Documentation Home <https://docs.yoctoproject.org/>`_
+- `Yocto Project Quick Build <https://www.yoctoproject.org/docs/current/brief-yoctoprojectqs/brief-yoctoprojectqs.html>`_
+- `Yocto Project Reference Manual <https://www.yoctoproject.org/docs/latest/ref-manual/ref-manual.html>`_