Add link to Apollo iOS

Author: shingt

README.md

@@ -1,6 +1,6 @@
 # GitHub-GraphQL-API-Example-iOS
 
-A simple iOS example app of GitHub GraphQL API using Apollo.
+A simple iOS example app of GitHub GraphQL API using [Apollo iOS](https://github.com/apollographql/apollo-ios).
 
 <img src="screenshot.png" width="200">