Add MEETMEBOOKID from r256019.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@258515 65c4cc65-6c06-0410-ace0-fbb531ad65f3

doc/tex/channelvariables.tex

@@ -883,6 +883,7 @@ ${MEETMESECS}              * Number of seconds a user participated in a MeetMe c
 ${CONF_LIMIT_TIMEOUT_FILE}   File to play when time is up.  Used with the L() option.
 ${CONF_LIMIT_WARNING_FILE}   File to play as warning if 'y' is defined.
                              The default is to say the time remaining.  Used with the L() option.
+${MEETMEBOOKID}            * This variable exposes the bookid column for a realtime configured conference bridge.
 \end{verbatim}
 
 \subsection{The VoiceMail() application}