Update google.md to reflect need for Google+ API for oauth integration;

clarify need for Kubernetes Engine API is only necessary for CI/CD
integration with GKE

doc/integration/google.md

@@ -35,7 +35,12 @@ In Google's side:
 
 1. You should now be able to see a Client ID and Client secret. Note them down
    or keep this page open as you will need them later.
-1. From the **Dashboard** select **ENABLE APIS AND SERVICES > Compute > Google Kubernetes Engine API > Enable**
+1. From the **Dashboard** select **ENABLE APIS AND SERVICES > Compute > Google+ API > Enable**
+1. To enable projects to access [Google Kubernetes Engine](../user/project/clusters/index.md), you must also
+   enable these APIs:
+   - Google Kubernetes Engine API
+   - Cloud Resource Manager API
+   - Cloud Billing API
 
 On your GitLab server: