Adding registration expectation

Adding registration expectation

Author: JackStromberg

articles/application-gateway/application-gateway-private-deployment.md

@@ -101,6 +101,9 @@ A list of all Azure CLI references for Private Link Configuration on Application
 
 ---
 
+>[!Note]
+>Feature registration may take up to 30 mintues to move from Registering to Registered status. 
+
 For more information about preview features, see [Set up preview features in Azure subscription](../azure-resource-manager/management/preview-features.md)
 
 ## Unregister from the preview