Update README.md

Update reference to gcp-jwt-go

README.md

@@ -37,7 +37,7 @@ See [the project documentation](https://godoc.org/github.com/dgrijalva/jwt-go) f
 
 This library publishes all the necessary components for adding your own signing methods.  Simply implement the `SigningMethod` interface and register a factory method using `RegisterSigningMethod`.  
 
-Here's an example of an extension that integrates with the Google App Engine signing tools: https://github.com/someone1/gcp-jwt-go
+Here's an example of an extension that integrates with multiple Google Cloud Platform signing tools (AppEngine, IAM API, Cloud KMS): https://github.com/someone1/gcp-jwt-go
 
 ## Compliance