Add note about keeping @mipmap/ic_launcher resource (#1804)

flutter_local_notifications/README.md

@@ -271,7 +271,7 @@ Note that when a full-screen intent notification actually occurs (as opposed to
 
 Before creating the release build of your app (which is the default setting when building an APK or app bundle) you will need to customise your ProGuard configuration file as per this [link](https://developer.android.com/studio/build/shrink-code#keep-code). Rules specific to the GSON dependency being used by the plugin will need to be added. These rules can be found [here](https://github.com/google/gson/blob/master/examples/android-proguard-example/proguard.cfg). Whilst the example app has a Proguard rules (`proguard-rules.pro`) [here](https://github.com/MaikuB/flutter_local_notifications/blob/master/flutter_local_notifications/example/android/app/proguard-rules.pro), it is recommended that developers refer to the rules on the GSON repository in case they get updated over time.
 
-⚠️ Ensure that you have configured the resources that should be kept so that resources like your notification icons aren't discarded by the R8 compiler by following the instructions [here](https://developer.android.com/studio/build/shrink-code#keep-resources). If you fail to do this, notifications might be broken. In the worst case they will never show, instead silently failing when the system looks for a resource that has been removed. If they do still show, you might not see the icon you specified. The configuration used by the example app can be found [here](https://github.com/MaikuB/flutter_local_notifications/blob/master/flutter_local_notifications/example/android/app/src/main/res/raw/keep.xml) where it is specifying that all drawable resources should be kept, as well as the file used to play a custom notification sound (sound file is located [here](https://github.com/MaikuB/flutter_local_notifications/blob/master/flutter_local_notifications/example/android/app/src/main/res/raw/slow_spring_board.mp3)).
+⚠️ Ensure that you have configured the resources that should be kept so that resources like your notification icons aren't discarded by the R8 compiler by following the instructions [here](https://developer.android.com/studio/build/shrink-code#keep-resources). If you have chosen to use `@mipmap/ic_launcher` as the notification icon (against the official Android guidance), be sure to include this in the `keep.xml` file. If you fail to do this, notifications might be broken. In the worst case they will never show, instead silently failing when the system looks for a resource that has been removed. If they do still show, you might not see the icon you specified. The configuration used by the example app can be found [here](https://github.com/MaikuB/flutter_local_notifications/blob/master/flutter_local_notifications/example/android/app/src/main/res/raw/keep.xml) where it is specifying that all drawable resources should be kept, as well as the file used to play a custom notification sound (sound file is located [here](https://github.com/MaikuB/flutter_local_notifications/blob/master/flutter_local_notifications/example/android/app/src/main/res/raw/slow_spring_board.mp3)).
 
 ## 🔧 iOS setup