Document -w option to shortlog

Noticed by Fredrik Noring.

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

Documentation/git-shortlog.txt

@@ -8,8 +8,8 @@ git-shortlog - Summarize 'git log' output
 SYNOPSIS
 --------
 [verse]
-git-log --pretty=short | 'git-shortlog' [-h] [-n] [-s] [-e]
+git-log --pretty=short | 'git-shortlog' [-h] [-n] [-s] [-e] [-w]
-git-shortlog [-n|--numbered] [-s|--summary] [-e|--email] [<committish>...]
+git-shortlog [-n|--numbered] [-s|--summary] [-e|--email] [-w[<width>[,<indent1>[,<indent2>]]]] [<committish>...]
 
 DESCRIPTION
 -----------
@@ -35,6 +35,12 @@ OPTIONS
 -e, \--email::
 	Show the email address of each author.
 
+-w[<width>[,<indent1>[,<indent2>]]]::
+	Linewrap the output by wrapping each line at `width`.  The first
+	line of each entry is indented by `indent1` spaces, and the second
+	and subsequent lines are indented by `indent2` spaces. `width`,
+	`indent1`, and `indent2` default to 76, 6 and 9 respectively.
+
 FILES
 -----
 

builtin-shortlog.c

@@ -8,7 +8,7 @@
 #include "mailmap.h"
 
 static const char shortlog_usage[] =
-"git-shortlog [-n] [-s] [-e] [<commit-id>... ]";
+"git-shortlog [-n] [-s] [-e] [-w] [<commit-id>... ]";
 
 static char *common_repo_prefix;
 static int email;