[operator-nexus] Update quickstarts-virtual-machine-deployment-arm.md

Adds warning to prevent users from submitting sensitive information via plaintext in cloud-init data.

Author: matthew-fuller

articles/operator-nexus/quickstarts-virtual-machine-deployment-arm.md

@@ -26,6 +26,9 @@ Before deploying the virtual machine template, let's review the content to under
 
 :::code language="json" source="includes/virtual-machine/virtual-machine-arm-template.json":::
 
+> [!IMPORTANT]
+> Please ensure that any sensitive data (e.g. secrets, passwords, private keys, etc.) are encrypted before they are submitted in the userdata or networkdata fields.
+
 Once you have reviewed and saved the template file named ```virtual-machine-arm-template.json```, proceed to the next section to deploy the template.
 
 ## Deploy the template