shortlog: document -e option

This shows e-mail address in addition to author's name.

Signed-off-by: Jeff King <peff@peff.net>
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]
+git-log --pretty=short | 'git-shortlog' [-h] [-n] [-s] [-e]
-git-shortlog [-n|--numbered] [-s|--summary] [<committish>...]
+git-shortlog [-n|--numbered] [-s|--summary] [-e|--email] [<committish>...]
 
 DESCRIPTION
 -----------
@@ -32,6 +32,9 @@ OPTIONS
 -s, \--summary::
 	Suppress commit description and provide a commit count summary only.
 
+-e, \--email::
+	Show the email address of each author.
+
 FILES
 -----