Update faq.yml

Author: Saisang

articles/virtual-desktop/faq.yml

@@ -4,6 +4,7 @@ metadata:
   description: Frequently asked questions and best practices for Azure Virtual Desktop.
   author: Heidilohr
   ms.topic: conceptual
+  ms.service: virtual-desktop
   ms.date: 03/09/2021
   ms.author: helohr 
   ms.custom: devx-track-azurepowershell