Update toc.yml

Author: j-martens

articles/machine-learning/toc.yml

@@ -92,8 +92,10 @@
     - name: Plan and manage costs
       href: concept-plan-manage-cost.md
     - name: Designer (drag-n-drop ML)
-      displayName: studio
-      href: concept-designer.md
+      items:
+      - name: Designer overview 
+        displayName: studio
+        href: concept-designer.md
       - name: Algorithm cheat sheet
         href: /azure/machine-learning/algorithm-cheat-sheet
       - name: How to select algorithms