nixos/azure: clarify how users work in basic example

nixos/maintainers/scripts/azure-new/README.md

@@ -33,3 +33,10 @@ img="/subscriptions/.../..." # use output from last command
 ...
 => booted
 ```
+
+## Future Work
+
+1. If the user specifies a hard-coded user, then the agent could be removed.
+   Probably has security benefits; definitely has closure-size benefits.
+   (It's likely the VM will need to be booted with a special flag. See:
+   https://github.com/Azure/azure-cli/issues/12775 for details.)

nixos/maintainers/scripts/azure-new/examples/basic/system.nix

@@ -8,6 +8,9 @@ in
     "${modulesPath}/virtualisation/azure-image.nix"
   ];
 
+  ## NOTE: This is just an example of how to hard-code a user.
+  ## The normal Azure agent IS included and DOES provision a user based
+  ## on the information passed at VM creation time.
   users.users."${username}" = {
     isNormalUser = true;
     home = "/home/${username}";