git-shortlog.txt: make SYNOPSIS match log, update OPTIONS

There are broadly two problems with the current SYNOPSIS.  First, it
completely omits the detail that paths can be specified.  Second, it
attempts to list all the options: this is futile as, in addition to
the options unique to it, it accepts all the options that git-rev-list
accepts.  In fixing these problems, make the SYNOPSIS consistent with
that in git-log.txt.  Also add the corresponding sections to OPTIONS.
Save adding the options from rev-list-options.txt for a later patch,
as it requires some work to pick out the options that are relevant to
shortlog.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
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] [-w]
-'git shortlog' [-n|--numbered] [-s|--summary] [-e|--email] [-w[<width>[,<indent1>[,<indent2>]]]] <commit>...
+git log --pretty=short | 'git shortlog' [<options>]
+'git shortlog' [<options>] [<revision range>] [[\--] <path>...]
 
 DESCRIPTION
 -----------
@@ -56,6 +56,21 @@ OPTIONS
 If width is `0` (zero) then indent the lines of the output without wrapping
 them.
 
+<revision range>::
+	Show only commits in the specified revision range.  When no
+	<revision range> is specified, it defaults to `HEAD` (i.e. the
+	whole history leading to the current commit).  `origin..HEAD`
+	specifies all the commits reachable from the current commit
+	(i.e. `HEAD`), but not from `origin`. For a complete list of
+	ways to spell <revision range>, see the "Specifying Ranges"
+	section of linkgit:gitrevisions[7].
+
+[\--] <path>...::
+	Consider only commits that are enough to explain how the files
+	that match the specified paths came to be.
++
+Paths may need to be prefixed with "\-- " to separate them from
+options or the revision range, when confusion arises.
 
 MAPPING AUTHORS
 ---------------