add posh article for Lb vmss

Author: asudbring

articles/load-balancer/TOC.yml

@@ -68,6 +68,8 @@
     items:
     - name: Use with an existing Azure Load Balancer - Portal
       href: configure-vm-scale-set-portal.md
+    - name: Use with an existing Azure Load Balancer - PowerShell
+      href: configure-vm-scale-set-powershell.md
     - name: Use with an existing Azure Load Balancer - CLI
       href: configure-vm-scale-set-cli.md
   - name: Upgrade a Basic Load Balancer to Standard Load Balancer