Update toc.yml

Author: eshashah-msft

articles/iot-hub-device-update/toc.yml

@@ -77,6 +77,8 @@ items:
     href: device-update-security.md
   - name: Network security
     href: network-security.md
+  - name: Data Encryption for Device Update for IoT Hub
+    href: device-update-data-encryption.md
   - name: Data privacy
     href: device-update-data-privacy.md
   - name: Device Update Supported Platforms