title: Any way to use Firebase google authentication in expo (create-react-native-app) without "eject" project
body: <p>As the question, for Login with google in firebase need to set google-service but if you create new react-native project with create-react-native-app there will have no "android" or "ios" folder (accept used "eject") so, anyone have a suggestion for me?
  However I've no idea for how to setting google-service in my project too (even I "eject" the project).</p>