added a note about problems converting the convertThis example to polymer
added a note about problems converting the convertThis example to polymer

dart-archive/dart-tutorials-samples,ronlobo/dart-tutorials-samples,kasperpeulen/dart-tutorials-samples,kasperpeulen/dart-tutorials-samples,kasperpeulen/dart-tutorials-samples,ronlobo/dart-tutorials-samples,ronlobo/dart-tutorials-samples,dart-archive/dart-tutorials-samples,dart-archive/dart-tutorials-samples