Document rev-list's option --merge

Signed-off-by: NUwe Zeisberger <Uwe_Zeisberger@digi.com>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Documentation/git-rev-list.txt

@@ -22,6 +22,7 @@ SYNOPSIS
 	     [ [\--objects | \--objects-edge] [ \--unpacked ] ]
 	     [ \--pretty | \--header ]
 	     [ \--bisect ]
+	     [ \--merge ]
 	     <commit>... [ \-- <paths>... ]
 
 DESCRIPTION
@@ -123,6 +124,10 @@ OPTIONS
 	topological order (i.e. descendant commits are shown
 	before their parents).
 
+--merge::
+	After a failed merge, show refs that touch files having a
+	conflict and don't exist on all heads to merge.
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>