Update README.md (#211)

Co-authored-by: Sam Stern <[email protected]>

Author: puf

README.md

@@ -11,10 +11,15 @@ only the data near certain locations, keeping your applications light and respon
 extremely large datasets.
 
 GeoFire is designed as a lightweight add-on to Firebase. To keep things simple, GeoFire stores data
-in its own format and its own location within your Firebase database. This allows your existing data
+in its own format and its own location within your Firebase Realtime Database. This allows your existing data
 format and Security Rules to remain unchanged while still providing you with an easy solution for geo
 queries.
 
+If you're looking to use this library with **Cloud Firestore**, see the documentation on 
+[implementing geoqueries on Firestore](https://firebase.google.com/docs/firestore/solutions/geoqueries).
+
+GeoFire is designed as a lightweight add-on to Firebase. To keep things simple, GeoFire stores data
+
 A compatible GeoFire client is also available for [Objective-C](https://github.com/firebase/geofire-objc)
 and [Java](https://github.com/firebase/geofire-java).