log --walk-reflog: documentation

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-rev-list.txt

@@ -190,6 +190,21 @@ limiting may be applied.
 	In addition to the '<commit>' listed on the command
 	line, read them from the standard input.
 
+--walk-reflogs::
+
+	Instead of walking the commit ancestry chain, walk
+	reflog entries from the most recent one to older ones.
+	When this option is used you cannot specify commits to
+	exclude (that is, '{caret}commit', 'commit1..commit2',
+	nor 'commit1...commit2' notations cannot be used).
++
+With '\--pretty' format other than oneline (for obvious reasons),
+this causes the output to have two extra lines of information
+taken from the reflog.  By default, 'commit@{Nth}' notation is
+used in the output.  When the starting commit is specified as
+'commit@{now}', output also uses 'commit@{timestamp}' notation
+instead.
+
 --merge::
 
 	After a failed merge, show refs that touch files having a