Add lack of Visual Designer in WinUI 3 (#4537)

* Add lack of Visual Designer in WinUI 3

* Update what-is-supported.md

* Update what-is-supported.md

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Co-authored-by: Steven White <[email protected]>

Author: soroshsabz

hub/apps/windows-app-sdk/migrate-to-windows-app-sdk/what-is-supported.md

@@ -40,3 +40,7 @@ WinUI 3 and the Windows App SDK are new technologies and, when compared to UWP,
 ## Performance considerations
 
 Today in version 1.3 of the Windows App SDK, launch speeds, RAM usage, and installation size of WinUI 3 apps are larger/slower than seen in UWP. We're actively working to improve this.
+
+## Visual Studio
+
+The **Design** tab of the XAML Designer in Visual Studio (and Blend for Visual Studio) doesn't currently support WinUI 3 projects (as of version 1.3 of the Windows App SDK). For more info, see [Create a UI by using XAML Designer](/visualstudio/xaml-tools/creating-a-ui-by-using-xaml-designer-in-visual-studio).