Added preview to TOC entry

Author: dlepow

articles/container-registry/TOC.yml

@@ -104,7 +104,7 @@
         href: container-registry-content-trust.md
       - name: Image scanning with Security Center (preview)
         href: ../security-center/azure-container-registry-integration.md?toc=/azure/container-registry/toc.json&bc=/azure/container-registry/breadcrumb/toc.json
-      - name: Encrypt registry data
+      - name: Encrypt registry data (preview)
         href: container-registry-customer-managed-keys.md
     - name: Registries and other Azure services
       expanded: false