Update README.md for Android Screenshare (#583)

Author: davidliu

README.md

@@ -239,7 +239,7 @@ In our example, we use the `flutter_background` package to handle this. In the a
 </manifest>
 ```
 
-Before starting the background service and enabling screen share, you **must** call `Helper.requestCapturePermission()` from `flutter_webrtc`, and only proceed if it returns true.
+Before starting the background service and enabling screen share, you **must** call `Helper.requestCapturePermission()` from `flutter_webrtc`, and only proceed if it returns true. [Refer to our example implementation for details.](https://github.com/livekit/client-sdk-flutter/blob/c97fa769260a3fefd146c0ee61e2ce5c30ce2010/example/lib/widgets/controls.dart#L159)
 
 #### iOS