docs: add note about Firestore iOS build times (#3365)
docs: add note about Firestore iOS build times (#3365)

Improved instructions for installation on iOS
firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire