Documentation/git-am: Document supported --patch-format options

The --patch-format option has been supported for a while but it is not
mentioned in the man page and the short help cannot tell the user what
the supported formats are. Add the option to the man page along with the
supported options.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-am.txt

@@ -12,9 +12,9 @@ SYNOPSIS
 'git am' [--signoff] [--keep] [--[no-]keep-cr] [--[no-]utf8]
 	 [--3way] [--interactive] [--committer-date-is-author-date]
 	 [--ignore-date] [--ignore-space-change | --ignore-whitespace]
-	 [--whitespace=<option>] [-C<n>] [-p<n>] [--directory=<dir>]
-	 [--exclude=<path>] [--include=<path>] [--reject] [-q | --quiet]
-	 [--[no-]scissors]
+	 [--whitespace=<option>] [-C<n>] [-p<n>] [--patch-format=<format>]
+	 [--directory=<dir>] [--exclude=<path>] [--include=<path>]
+	 [--reject] [-q | --quiet] [--[no-]scissors]
 	 [(<mbox> | <Maildir>)...]
 'git am' (--continue | --skip | --abort)
 
@@ -97,6 +97,12 @@ default.   You can use `--no-utf8` to override this.
 	program that applies
 	the patch.
 
+--patch-format::
+	By default the command will try to detect the patch format
+	automatically. This option allows the user to bypass the automatic
+	detection and specify the patch format that the patch(es) should be
+	intepreted as. Valid formats are mbox, stgit, stgit-series and hg.
+
 -i::
 --interactive::
 	Run interactively.