Add tools page

Author: craigshoemaker

articles/sre-agent/toc.yml

@@ -22,4 +22,8 @@ items:
     - name: Troubleshooting
       href: troubleshoot.md
     - name: Billing
-      href: billing.md
+      href: billing.md
+- name: Reference
+  items:
+    - name: Tools used by Azure SRE Agent
+      href: tools.md