Improve README and fix #702
Improve README and fix #702

firebase/FirebaseUI-Android,samtstern/FirebaseUI-Android,JosefHruska/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,JosefHruska/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,samtstern/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,samtstern/FirebaseUI-Android,firebase/FirebaseUI-Android,firebase/FirebaseUI-Android