Document 'git (rev-list|log) --merges'

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rev-list.txt

@@ -14,6 +14,7 @@ SYNOPSIS
 	     [ \--max-age=timestamp ]
 	     [ \--min-age=timestamp ]
 	     [ \--sparse ]
+	     [ \--merges ]
 	     [ \--no-merges ]
 	     [ \--first-parent ]
 	     [ \--remove-empty ]

Documentation/rev-list-options.txt

@@ -201,6 +201,10 @@ endif::git-rev-list[]
 
 	Stop when a given path disappears from the tree.
 
+--merges::
+
+	Print only merge commits.
+
 --no-merges::
 
 	Do not print commits with more than one parent.