[docs] start of app/core documentation

docs/_sidebar.md

@@ -9,6 +9,10 @@
  - [Guidelines](/contributing/guidelines)
  - [Testing](/contributing/testing)
 
+- Core
+ - [App](/core/app)
+ - [Firebase](/core/firebase)
+
 - Modules
  - [Admob](/modules/admob)
  - [Analytics](/modules/analytics)

docs/core/app.md

@@ -0,0 +1,34 @@
+# App
+
+RNFirebase supports both initializing apps natively and also via js code over the RN bridge.
+
+Apps initialized natively are available immediately at app runtime, there is no need to call `initializeApp` for them.
+
+For example, to access the default app initialized via the `Google-Services` `plist` or `json` file:
+```javascipt
+import firebase from 'react-native-firebase';
+
+const defaultApp = firebase.app();
+
+defaultApp.database().ref('foobar').once('value', (snapshot) => {
+  // snapshot from default app
+});
+
+// get the default app name/options that were initialized natively
+console.log("name", defaultApp.name);
+console.log("apiKey", defaultApp.options.apiKey);
+console.log("applicationId", defaultApp.options.applicationId);
+console.log("databaseUrl", defaultApp.options.databaseUrl);
+console.log("messagingSenderId", defaultApp.options.messagingSenderId);
+console.log("projectId", defaultApp.options.projectId);
+console.log("storageBucket", defaultApp.options.projectId);
+```
+
+
+TODO api ref docs:
+
+ - name: String
+ - options: Object
+ - delete(): Promise
+
+

docs/core/firebase.md

@@ -0,0 +1,10 @@
+# Firebase
+
+TODO api ref docs:
+
+ - apps(): Array<FirebaseApp>
+ - app(): FirebaseApp
+ - initializeApp(): FirebaseApp
+ - setLogLevel()
+ - SDK_VERSION: String
+ - googleApiAvailability: Object