Update TOC.yml

Add migration page to the TOC

Author: bpevans

powerapps-docs/developer/common-data-service/TOC.yml

@@ -412,6 +412,8 @@
     href: xrm-tooling/
   - name: Discover user organizations
     href: discovery-service.md
+  - name: Modify existing code to use the Discovery Web API
+    href: discovery-orgsdk-to-webapi.md
 - name: Best practices
   href: best-practices/index.md
 - name: Online Management API