Improve documentation for inclusion into Oniro

Related to eclipse/oniro-core/docs#140 (closed)

docs/supported-technologies/openharmony-image.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+.. include:: ../definitions.rst
+
+OpenHarmony Image
+#################
+
+Oniro Project can include OpenHarmony compatibility in the predefined images by
+enabling `openharmony` distro feature and adding it to the images.
+
+See :ref:`Building with OpenHarmony compatibility <Building with OpenHarmony>` in
+Quick Build instructions for details on how to do this.