Improve storage docs (#1011)
Improve storage docs (#1011)

Fixes #971
firebase/FirebaseUI-Android,samtstern/FirebaseUI-Android,samtstern/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,firebase/FirebaseUI-Android,samtstern/FirebaseUI-Android