Update cheatsheets

tldr/flutterfire

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# flutterfire
+
+> Configure a Firebase project for your Flutter app.
+> Note: Requires Firebase CLI and FlutterFire CLI to be installed.
+> More information: <https://firebase.google.com/docs/flutter/setup>.
+
+- Initialize and configure Firebase for your current Flutter app:
+
+`flutterfire configure`
+
+- Specify platforms (iOS, Android, web) to support:
+
+`flutterfire configure --platforms {{ios,android,...}}`
+
+- Use a specific Firebase project:
+
+`flutterfire configure --project {{project_id}}`