supportConnectionService is not an async function!

Removed "async" from supportConnectionService since it's not asynchronous.

Author: linus-komnick

README.md

@@ -586,7 +586,7 @@ await RNCallKeep.setAudioRoute(uuid, routeName);
 - `routeName`: String
   - AudioRoute.name. 
 
-### supportConnectionService (async)
+### supportConnectionService
 
 _This feature is available only on Android._