[ACA] Add link to Azure Front Door supported regions.

Author: v-jaswel

articles/container-apps/how-to-integrate-with-azure-front-door.md

@@ -36,6 +36,8 @@ In this article, you learn how to connect directly from Azure Front Door to your
 
 - This feature is only supported for workload profile environments.
 
+- This feature is only supported in [certain regions](/azure/frontdoor/private-link#region-availability).
+
 For more information about prerequisites and setup, see [Quickstart: Deploy your first container app with containerapp up](get-started.md?tabs=bash).
 
 ## Set environment variables