Add doc tags to sample app
Add doc tags to sample app

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GoogleCloudPlatform/appengine-gcs-client,GoogleCloudPlatform/appengine-gcs-client,aozarov/appengine-gcs-client,aozarov/appengine-gcs-client,GoogleCloudPlatform/appengine-gcs-client,aozarov/appengine-gcs-client