Update globals.yml Docker registry example notes

Note that the 'docker_registry_password' can also be set in
passwords.yml since most people may want to use Ansible's vault to
secure their password files.

TrivialFix
Change-Id: I8980aaaf7af97c1751012de427d20ba09cda1252

etc/kolla/globals.yml

@@ -44,7 +44,8 @@ kolla_internal_vip_address: "10.10.10.254"
 ####################
 # Docker options
 ####################
-### Example: Private repository with authentication
+# Below is an example of a private repository with authentication. Note the
+# Docker registry password can also be set in the passwords.yml file.
 
 #docker_registry: "172.16.0.10:4000"
 #docker_namespace: "companyname"