Document git-instaweb start/stop/restart

The flags --start, --stop, and --restart can be used without the "--".
Document this feature.
Signed-off-by: NJared Hance <jaredhance@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-instaweb.txt

@@ -49,15 +49,18 @@ OPTIONS
 	linkgit:git-web--browse[1] for more information about this. If
 	the script fails, the URL will be printed to stdout.
 
+start::
 --start::
 	Start the httpd instance and exit.  This does not generate
 	any of the configuration files for spawning a new instance.
 
+stop::
 --stop::
 	Stop the httpd instance and exit.  This does not generate
 	any of the configuration files for spawning a new instance,
 	nor does it close the browser.
 
+restart::
 --restart::
 	Restart the httpd instance and exit.  This does not generate
 	any of the configuration files for spawning a new instance.