Update old information on the website playground

website/playground/new-samples/interacting-with-the-editor/listening-to-key-events/sample.js

@@ -7,4 +7,5 @@ var myBinding = editor.addCommand(monaco.KeyCode.F9, function() {
 	alert('F9 pressed!');
 });
 
-// When cleaning up remember to call myBinding.dispose()
+// You can't dispose `addCommand`
+// If you need to dispose it you might use `addAction` or `registerCommand`