Clarify SDK compatibility
Clarify SDK compatibility

Fixes #218
SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,samtstern/FirebaseUI-Android,samtstern/FirebaseUI-Android,firebase/FirebaseUI-Android,samtstern/FirebaseUI-Android,firebase/FirebaseUI-Android,MaciejCiemiega/FirebaseUI-Android,JosefHruska/FirebaseUI-Android,firebase/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,JosefHruska/FirebaseUI-Android