Updated clientacl docs to resolve 6802.

Added a note specifying that the user has to modify permissions of the log file, or disable logging. I did not add an additional command as the user may wish to configure advanced ACL settings to prohibit access as opposed to simply setting 777 permissions as that could be a security concern since data has to be written into the logs. This resolves https://github.com/saltstack/salt/issues/6802.