Change usage of pipe to comma in UserEvent docs.

Change the example usage of pipe as a separator to comma in the UserEvent
documentation.

(closes issue #16961)
Reported by: jlpedrosa

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@253345 65c4cc65-6c06-0410-ace0-fbb531ad65f3