Add OpenHarmony documentation

Closes #140 (closed)

overview/oniroproject-vision.rst

@@ -44,6 +44,24 @@ able to choose from Java, Extensible Markup Language (XML), C/C++, JavaScript
 (JS), Cascading Style Sheets (CSS), and HarmonyOS Markup Language (HML) to
 develop applications for |main_project_name|.
 
+OpenHarmony Compatibility
+-------------------------
+
+|main_project_name| will be OpenHarmony compatible. It will include the services
+and frameworks required by OpenHarmony specification, and provide the APIs
+required by OpenHarmony specification, so that you can develop products that can
+interoperate with other OpenHarmony products and be certified as OpenHarmony
+compatible.
+
+OpenHarmony compatibility will enable required OpenHarmony features in the
+kernel layer, system services layer and framework layer, allowing the addition
+of OpenHarmony compatible applications.
+
+Due to the inherent modularity of the Oniro build system (OpenEmbedded),
+individual projects will be able to pick and choose from the OpenHarmony
+compatibility features, allowing to build products with just the parts that are
+needed.
+
 Technical Architecture
 ----------------------