Document that BT servers on Android and WinRT only support RFCOMM

Change-Id: Ic93d086cc6b6549e8de90f01a0bba5913207d7e5
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

src/bluetooth/qbluetoothserver.cpp

@@ -64,6 +64,7 @@ QT_BEGIN_NAMESPACE
     Call serverPort() to get the channel number that is being used.
 
     If the \l QBluetoothServiceInfo::Protocol is not supported by a platform, \l listen() will return \c false.
+    Android and WinRT only support RFCOMM for example.
 
     \sa QBluetoothServiceInfo, QBluetoothSocket
 */