adding toc entry

Author: bandersmsft

articles/cost-management-billing/costs/toc.yml

@@ -22,6 +22,8 @@
     items:
     - name: Azure Cost Management best practices
       href: cost-mgt-best-practices.md
+    - name: Choose between Cost Management and Cloudyn
+      href: ../understand/choose-between-azure-cost-management-cloudyn.md
     - name: Understand Cost Management data
       href: understand-cost-mgt-data.md
     - name: Understand and work with scopes