Update Freeze.md

Author: LiangTheDev

specs/Freeze.md

@@ -13,9 +13,15 @@ For an Universal Windows Platform app, the app calls the API in suspended event
 async protected void OnSuspending(object sender, SuspendingEventArgs args)
 {
     SuspendingDeferral deferral = args.SuspendingOperation.GetDeferral();
+    webView.Visibility = false;
     await webView.CoreWebView2.TryFreezeAsync();
     deferral.Complete();
 }
+async protected void OnSuspending(object sender, Object args)
+{
+    webView.CoreWebView2.Unfreeze();
+    webView.Visibility = true;
+}
 ```
 ## Win32 C++
 As unfreeze is very fast and automatically happens when WebView becomes visible, the app can generaly immediately call `TryFreeze` when a WebView becomes invisible.