Updated app delegate code in walkthrough doc

GoneBananas/Walkthrough.md

@@ -46,12 +46,12 @@ Add a new class named GoneBananasApplicationDelegate with the following implemen
             {
                 application.PreferMultiSampling = false;
                 application.ContentRootDirectory = "Content";
-
-                mainWindow.SupportedDisplayOrientations = CCDisplayOrientation.Portrait;
-
                 application.ContentSearchPaths.Add("hd");
 
                 CCSimpleAudioEngine.SharedEngine.PreloadEffect ("Sounds/tap");
+                
+                CCSize winSize = mainWindow.WindowSizeInPixels;
+                mainWindow.SetDesignResolutionSize(winSize.Width, winSize.Height, CCSceneResolutionPolicy.ExactFit);
 
                 CCScene scene = GameStartLayer.GameStartLayerScene(mainWindow);
                 mainWindow.RunWithScene (scene);