Update TOC.yml

Author: abinav2307

articles/cosmos-db/mongodb/vcore/TOC.yml

@@ -48,8 +48,12 @@
       href: indexing.md
     - name: Reliability
       href: /azure/reliability/reliability-cosmos-mongodb?toc=/azure/cosmos-db/mongodb/vcore/toc.json
-    - name: Compute and storage
-      href: compute-storage.md 
+    - name: Scalability
+      items: 
+       - name: Scalability Overview
+       - href: scalability-overview.md
+       - name: Compute and Storage
+       - href: compute-storage.md 
     - name: Migration options
       href: migration-options.md
     - name: Service limits