Add MARS PS to TOC

Author: David Curwin

articles/backup/toc.yml

@@ -393,8 +393,10 @@
     href: /dotnet/api/microsoft.azure.management.recoveryservices.backup
   - name: Azure CLI
     href: /cli/azure/backup?view=azure-cli-latest
-  - name: PowerShell
+  - name: Azure PowerShell
     href: /powershell/module/az.recoveryservices
+  - name: Powershell – Azure Backup Agent
+    href: /powershell/module/msonlinebackup
   - name: REST - Backup
     href: /rest/api/backup/
   - name: REST - Recovery Services vault