Update the README documentation to correctly describe which CLI command you should
use when attempting to get help from the CLI.

(closes issue #16064)
Reported by: thedavidfactor
Patches:
      readme.patch uploaded by thedavidfactor (license 903)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@225515 65c4cc65-6c06-0410-ace0-fbb531ad65f3