test-vm: Echo help message for shutdown alias

hosts/test-vm/configuration.nix

@@ -34,6 +34,8 @@
     # Resize terminal to host terminal size
     environment.loginShellInit = ''
       ${pkgs.xterm}/bin/resize
+
+      echo alias 'sd' can be used to shutdown the VM
     '';
 
     environment.interactiveShellInit = ''