simplify loop

docs/06-data-encryption-keys.md

@@ -35,7 +35,7 @@ EOF
 Copy the `encryption-config.yaml` encryption config file to each controller instance:
 
 ```sh
-for instance in controller-0 controller-1 controller-2; do
+for instance in controller-{0..2}; do
   gcloud compute scp encryption-config.yaml ${instance}:~/
 done
 ```