Added pointer to Graph-specific guidelines.

Author: garethj-msft

README.md

@@ -9,6 +9,9 @@ We further hope that these guidelines may encourage other organizations to creat
 ### Additional guidance for Azure service teams
 Azure service teams should reference the companion documents, [Azure REST API Guidelines](./azure/Guidelines.md) and [Considerations for Service Design](./azure/ConsiderationsForServiceDesign.md), when building or modifying their services. These documents provide a refined set of guidance targeted specifically for Azure services. For more information please refer to the [README](./azure/README.md) in the Azure folder. 
 
+### Additional guidance for Microsoft Graph service teams
+Graph service teams should reference the companion document, [Graph REST API Guidelines](./graph/GuidelinesGraph.md) when building or modifying their services. This document and the associated pattern catalog provides a refined set of guidance targeted specifically for Microsoft Graph services.
+
 [![License: CC BY 4.0](https://img.shields.io/badge/License-CC%20BY%204.0-lightgrey.svg)](https://creativecommons.org/licenses/by/4.0/)
 
 ## Code of Conduct