Added a note about contributing to this project

Author: javiereguiluz

README.md

@@ -48,12 +48,31 @@ $ cd symfony-demo/
 $ php app/console server:run
 ```
 
-This command will start a web server for the Symfony application. Now you can access
-the application in your browser at <http://localhost:8000>. You can stop the built-in
-web server by pressing `Ctrl + C` while you're in the terminal.
+This command will start a web server for the Symfony application. Now you can
+access the application in your browser at <http://localhost:8000>. You can
+stop the built-in web server by pressing `Ctrl + C` while you're in the
+terminal.
 
 > **NOTE**
 >
 > If you're using PHP 5.3, configure your web server to point at the `web/`
 > directory of the project. For more details, see:
 > http://symfony.com/doc/current/cookbook/configuration/web_server_configuration.html
+
+Contributing
+------------
+
+Contributions to this project are welcome. Send us your ideas, code reviews,
+pull requests and feature requests to help us improve this project. All
+contributions must follow the [usual Symfony contribution requirements](http://symfony.com/doc/current/contributing/index.html).
+
+This project manages its web assets in a special way to allow them to work
+without configuring any option, installing any tool or executing any command.
+If your contribution changes CSS styles or JavaScript code in any way, make
+sure to regenerate the `web/css/app.css` and `web/js/app.js` files. To do so,
+uncomment the Assetic blocks in the `app/Resources/views/base.html.twig` and
+execute the following command:
+
+```bash
+$ php app/console assetic:dump --no-debug
+```