Document merge.branchdesc configuration variable
Document merge.branchdesc configuration variable

This was part of the "branch description" feature in the larger
"help people communicate better during their pull based workflow"
topic, but was never documented.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git