add example of updating inside click

samples/ControlCatalog/MainWindow.xaml.cs

@@ -29,6 +29,14 @@ namespace ControlCatalog
 
             DataContext = new MainWindowViewModel(_notificationArea);
             _recentMenu = ((NativeMenu.GetMenu(this).Items[0] as NativeMenuItem).Menu.Items[2] as NativeMenuItem).Menu;
+
+            var fileMenu = (NativeMenu.GetMenu(this).Items[0] as NativeMenuItem).Menu;
+            
+            fileMenu.NeedsUpdate += (sender, e)=>
+            {
+                fileMenu.Items.Add(new NativeMenuItem("Test 1"));
+            };
+
             var mainMenu = this.FindControl<Menu>("MainMenu");
             mainMenu.AttachedToVisualTree += MenuAttached;
         }