Update example to remove passing in aws creds on command line.

playbooks/adhoc/s3_registry/s3_registry.yml

@@ -1,7 +1,7 @@
 ---
 # This playbook creates an S3 bucket named after your cluster and configures the docker-registry service to use the bucket as its backend storage.
 # Usage:
-#  ansible-playbook s3_registry.yml -e accesskey="S3 aws access key" -e secretkey="S3 aws secret key" -e clusterid="mycluster"
+#  ansible-playbook s3_registry.yml -e clusterid="mycluster"
 #
 # The AWS access/secret keys should be the keys of a separate user (not your main user), containing only the necessary S3 access role.
 # The 'clusterid' is the short name of your cluster.