Added new topic to TOC

Author: phecke

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

@@ -33,6 +33,8 @@
       href: column-comparison.md
     - name: FetchXML search item limit
       href: quick-find-limit.md
+    - name: Improve FetchXML request performance
+      href: fetchxml-performance.md
   - name: "Use SQL to query data (Preview)"
     href: cds-sql-query.md
   - name: Saved Queries