Add mongodb driver as a requirement
As described here : #84 , composer will fail if the mongo extension is not installed.
|@@ -28,7 +28,8 @@ Requirements|
|Symfony is only supported on PHP 5.3.2 and up. To check the compatibility of|
|your environment with Symfony, you can run the `web/check.php` script, bundled|
|-with this sandbox.|
|+with this sandbox. Also, you will need the mongodb driver for php, provided by|
|+the mongo php extension.|