* Added a note to GCE auto-join credentials option
Simply added a note to remind users that putting a json file in the config-dir will make consul parse it as a config file.
Hope to help someone else avoid wasting a day because of these errors:
==> Error parsing /etc/consul.d/credentials.json: 10 error(s) occurred: * invalid config key private_key
* Updated according to style guidelines
Co-Authored-By: delamart <erik@delamarter.ch>