docs: Add instructions for iOS AppDelegate.swift on react-native 0.77 (#8265)

* Added instructions for iOS AppDelegate.swift on react-native 0.77
* style(lint): `yarn lint:markdown --write`

---------

Co-authored-by: Mike Hardy <github@mikehardy.net>

Author: bigriot

docs/index.md

@@ -174,7 +174,30 @@ Select the downloaded `GoogleService-Info.plist` file from your computer, and en
 
 ![Select 'Copy Items if needed'](https://prismic-io.s3.amazonaws.com/invertase%2F7d37e0ce-3e79-468d-930c-b7dc7bc2e291_unknown+%282%29.png)
 
-#### Configure Firebase with iOS credentials
+#### Configure Firebase with iOS credentials (react-native 0.77+)
+
+To allow Firebase on iOS to use the credentials, the Firebase iOS SDK must be configured during the bootstrap phase of your application.
+
+To do this, open your `/ios/{projectName}/AppDelegate.swift` file and add the following:
+
+At the top of the file, import the Firebase SDK right after `'import ReactAppDependencyProvider'`:
+
+```
+import Firebase
+```
+
+Within your existing `didFinishLaunchingWithOptions` method, add the following to the top of the method:
+
+```
+  override func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
+  // Add me --- \/
+  FirebaseApp.configure()
+  // Add me --- /\
+  // ...
+}
+```
+
+#### Configure Firebase with iOS credentials (react-native < 0.77)
 
 To allow Firebase on iOS to use the credentials, the Firebase iOS SDK must be configured during the bootstrap phase of your application.