Update toc.yml

Author: jaesoni

articles/application-gateway/toc.yml

@@ -69,6 +69,8 @@
     href: application-gateway-autoscaling-zone-redundant.md
   - name: WebSocket support
     href: application-gateway-websocket.md
+  - name: DNS resolution details
+    href: application-gateway-dns-resolution.md
   - name: Ingress for AKS
     href: ingress-controller-overview.md
   - name: Understanding pricing