Fix database README.md
Fix database README.md

Fixes #172
firebase/FirebaseUI-Android,samtstern/FirebaseUI-Android,JosefHruska/FirebaseUI-Android,samtstern/FirebaseUI-Android,samtstern/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,JosefHruska/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,MaciejCiemiega/FirebaseUI-Android,firebase/FirebaseUI-Android,firebase/FirebaseUI-Android