Link to asp.net core what's new (#16780)

Happy to see this go live.

Author: BillWagner

docs/whats-new/index.yml

@@ -46,6 +46,8 @@ landingContent:
     linkLists:
       - linkListType: whats-new
         links:
+          - text: ASP.NET Core docs updates
+            url: https://docs.microsoft.com/aspnet/core/whats-new/
           - text: Xamarin docs updates
             url: https://docs.microsoft.com/xamarin/whats-new/
           - text: .NET Core release notes