DO NOT MERGE Fix 5389442 RemoteControlClient javadoc

Extend RemoteControlClient class description with an example
 of instance creation showing how the PendingIntent is created
 and how it uses the same ComponentName as the one used
 in AudioManager.registerMediaButtonEventReceiver()

Change-Id: I1af61ddbf5cfb9160ea5b814bed7b881d51b7eff