adding new article

Author: aahill

articles/ai-services/agents/toc.yml

@@ -52,6 +52,8 @@ items:
           href: concepts/tracing.md
         - name: Content filtering
           href: ../openai/how-to/content-filters.md?context=/azure/ai-services/agents/context/context
+        - name: Use virtual networks
+          href: how-to/virtual-networks.md
 - name: Responsible AI
   items:
     - name: Transparency note