Add quick-start-contribution-onboarding.rst and improve gitlab.rst

@kristis and I prepared documentation file which describes how to contribute to the Oniro Project

Closes #150 (closed)

Signed-off-by: Grzegorz Gwóźdź grzegorz.gwozdz@huawei.com

contributing/gitlab.rst

@@ -21,6 +21,24 @@ with proposed changes and raise a merge request against the forked repository.
 More generic information you can find on the Gitlab's documentation as part of
 `"Merge requests workflow" <https://docs.gitlab.com/ee/development/contributing/merge_request_workflow.html>`_.
 
+Git setup
+*********
+
+Clone your fork locally, enter its directory and set:
+
+.. code-block:: bash
+
+    $ git config --local user.email <your_eclipse_account_email>
+    $ git config --local user.name <your_eclipse_full_name>  
+
+
+To push and pull over HTTPS with Git using your account, you must set a password
+or `a Personal Access Token <https://docs.gitlab.com/ee/user/profile/personal_access_tokens.html>`_
+.
+
+If you want to push or pull repositories using SSH, you have to
+`add a SSH key <https://docs.gitlab.com/ee/user/ssh.html>`_ to your profile.
+
 Commit Guidelines
 *****************
 
@@ -145,3 +163,21 @@ is to maintain the RestructuredText file format. Text files that are not meant t
 as part of the project's documentation can be written in `Markdown <https://daringfireball.net/projects/markdown/>`_.
 For example, a repository ``README`` file can be written in Markdown as it
 doesn't end up compiled in the project-wide documentation.
+
+Creating merge requests
+-----------------------
+
+Once your changes have been pushed to your fork, you are ready to prepare a merge request.
+
+1. Go to your repository in an internet browser. 
+
+#. Create a merge request by clicking ``Merge Requests`` on left toolbar
+   and press ``New merge request``. Add an explainable description and create a merge request.
+   Alternatively, you can enter the website of your fork. You should see a message that you 
+   pushed your branch to the repository. In the same section you can press ``Create merge request``.
+#. Before merging, it has to be reviewed and approved by 2 of |main_project_name| repository
+   maintainers. Read their review and add any required changes to your merge request. 
+#. After you polish your merge request, the maintainers will run the pipelines which check
+   if your changes do not break the project and approve them. If everything is correct, your work
+   is merged to the main project. Remember that each commit of the merge request should be a minimum,
+   self-contained building block.