add iOS setup step 3b. remove RCTBridgeDelegate from AppDelegate.h (#4868)

docs/docs/Installing.md

 	@end
 	```
 
-3a. If, in Xcode, you see the following error message in `AppDelegate.m` next to `#import "RCTBundleURLProvider.h": 
+3a. If, in Xcode, you see the following error message in `AppDelegate.m` next to `#import "RCTBundleURLProvider.h"`: 
 ```
 ! 'RCTBundleURLProvider.h' file not found
 ```
 
 To make the `React` scheme available to your project, run `npm install -g react-native-git-upgrade` followed by `react-native-git-upgrade`. Once this is done, you can click back to the menu in Xcode: `Product -> Scheme -> Manage Schemes`, then click '+' to add a new scheme. From the `Target` menu, select "React", and click the checkbox to make the scheme `shared`. This should make the error disappear.
 
+3b. If, in Xcode, you see the following warning message in `AppDelegate.m` next to `#import "@implementation AppDelegate"`:
+```
+Class 'AppDelegate' does not conform to protocol 'RCTBridgeDelegate'
+```
+You can remove `RCTBridgeDelegate` from this file: `AppDelegate.h`:
+```diff
+- #import <React/RCTBridgeDelegate.h>
+- @interface AppDelegate : UIResponder <UIApplicationDelegate, RCTBridgeDelegate>
++ @interface AppDelegate : UIResponder <UIApplicationDelegate>
+	...
+```
+
 ## Android
 
 > Make sure your Android Studio installation is updated. We recommend editing `gradle` and `java` files in Android Studio as the IDE will suggest fixes and point out errors, this way you avoid most common pitfalls.