Fix incorrect client ACL documentation

Tested this by setting up a local Vagrant instance using the following
procedure:
 1. Made a fresh minion/master install (using salt-bootstrap) of version
    2014.1.10.
 2. Adding a `test.ping` ACL rule for the `vagrant` user.
 3. Asserting that I couldn't execute `salt '*' test.ping'` as `vagrant`
    user.
 4. Applying `chmod 755 /var/cache/salt /var/cache/salt/master/jobs
    /var/run/salt /var/run/salt/master`.
 5. Verifying that `salt '*' test.ping'` now works.

Fixes #16318.
Merge pull request #16389 from JensRantil/fix-client-acl-doc

Fix incorrect client ACL documentation