'queue add member' help text correction

You are adding dial strings to the queue, not channels. An aribitrary string
could be used, but you are typically referencing a channel. Correcting the
command help text.

(issue ASTERISK-22263)
(closes issue ASTERISK-22263)
Reported By: Rusty Newton
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Merged revisions 398884 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 398885 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 398886 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@398887 65c4cc65-6c06-0410-ace0-fbb531ad65f3