Improve comment in app.yaml

Author: sepehre

endpoints/getting-started/app.yaml

@@ -3,6 +3,10 @@ env: flex
 
 endpoints_api_service:
   # The following values are to be replaced by information from the output of
-  # 'gcloud service-management deploy openapi.yaml' command.
-  name: ENDPOINTS SERVICE-NAME
-  config_id: ENDPOINTS CONFIG-ID
+  # 'gcloud service-management deploy openapi.yaml' command. If you have
+  # previously run the deploy command, you can list your existing configuration
+  # ids using the 'configs list' command as follows:
+  # 'gcloud service-management configs list --service=echo-api.endpoints.[PROJECT-ID].cloud.goog'
+  # where echo-api.endpoints.[PROJECT-ID].cloud.goog is your Endpoints service name.
+  name: ENDPOINTS SERVICE NAME
+  config_id: ENDPOINTS CONFIG ID