Added comment about sip transports in config file

darcs-hash:20081208161221-58252-1b03639537ae888e56f02f4d142d61bd79871929
sip_im_session and sip_im_conference: changed registration expires back to 300

darcs-hash:20081208161515-b2873-b0f770ec98b8df71c3cb38d96327b3c41de2e764