docs: behaviour.md - useful fullscreen tips (#928)

docs-react-native/react-native/docs/android/behaviour.md

@@ -191,7 +191,7 @@ notifee.displayNotification({
 });
 ```
 
-and, by adding `showWhenLocked` and `turnScreenOn` to your activity:
+and, by adding `showWhenLocked` and `turnScreenOn` to your activity in android/app/src/main/AndroidManifest.xml:
 ```xml
   <activity
     ...
@@ -200,6 +200,8 @@ and, by adding `showWhenLocked` and `turnScreenOn` to your activity:
   />
 ```
 
+> After making these changes, be sure to run `cd android` and `./gradlew clean`, then re-install the app.
+
 Running this code, Notifee will attempt to launch the activity when the notification is displayed.
 
 > Please note that the notification may be shown as a heads-up notification, instead of a full-screen notification, while the user is using the device.