Add note about returning custom views in maintenance mode. Closes lar…

…avel#266.

configuration.md

@@ -74,4 +74,11 @@ To enable maintenance mode, simply execute the `down` Artisan command:
 
 To disable maintenance mode, use the `up` command:
 
- php artisan up
+ php artisan up
+
+To show a custom view when your application is in maintenance mode, you may add something like the following to your application's `app/start/global.php` file:
+
+ App::down(function()
+ {
+  return Response::view('maintenance', array(), 503);
+ })