updated readme to include GraphQL

Author: isabelatkinson

readme.md

@@ -5,6 +5,7 @@ This sample app is intended to be used by following the
 Stitch docs. It demonstrates the process of building a React Web app that 
 connects to the Stitch backend and uses Atlas for data storage. 
 
-We also have [iOS](https://github.com/mongodb-university/stitch-tutorial-todo-ios) 
-and [Android](https://github.com/mongodb-university/stitch-tutorial-todo-android) 
+We also have [iOS](https://github.com/mongodb-university/stitch-tutorial-todo-ios),
+[Android](https://github.com/mongodb-university/stitch-tutorial-todo-android) and
+[GraphQL](https://github.com/mongodb-university/stitch-tutorial-todo-graphql)
 versions.