Adding documentation regarding imapfolder, imapgreetings, and greetingsfolder options

in voicemail.conf

(closes issue #11133, reported by selsky, patched by blitzrage)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@89075 65c4cc65-6c06-0410-ace0-fbb531ad65f3