fmt-merge-msg-config.txt

merge.branchdesc::
	In addition to branch names, populate the log message with
	the branch description text associated with them.  Defaults
	to false.

merge.log::
	In addition to branch names, populate the log message with at
	most the specified number of one-line descriptions from the
	actual commits that are being merged.  Defaults to false, and
	true is a synonym for 20.