Add nano save/close instruction to match ARM32 doc

Match ARM32 doc for Linux nano editor instruction

Author: theangellmethod

articles/iot-edge/how-to-install-iot-edge-linux.md

@@ -118,6 +118,10 @@ The edge device can be configured manually using a [device connection string][ln
      registration_id: "{registration_id}"
    ```
 
+Save and close the file. 
+
+   `CTRL + X`, `Y`, `Enter`
+
 After entering the provisioning information in the configuration, restart the daemon:
 
 ```cmd/sh