Add "Check for Updates" menu item

DesktopClock/MainWindow.xaml

@@ -88,6 +88,9 @@
             <MenuItem Click="MenuItemAbout_OnClick"
                       Header="_About..." />
 
+            <MenuItem Click="MenuItemCheckForUpdates_OnClick"
+                      Header="Check for _Updates..." />
+
             <MenuItem Click="MenuItemExit_OnClick"
                       Header="E_xit" />
         </ContextMenu>

DesktopClock/MainWindow.xaml.cs

@@ -103,6 +103,11 @@ namespace DesktopClock
             }.ShowDialog();
         }
 
+        private void MenuItemCheckForUpdates_OnClick(object sender, RoutedEventArgs e)
+        {
+            Process.Start("https://github.com/danielchalmers/DesktopClock/releases");
+        }
+
         private void MenuItemExit_OnClick(object sender, RoutedEventArgs e)
         {
             Close();