[Cookbook] add cookbook article for the server:run command

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#3465)
| Applies to    | all
| Fixed tickets | 
What about a really small section about VM's. Something like, which just comes from a few times of experience (so, I'll want someone else to give me a :thumbsup: on this):

```sphinx
Using the built-in web server from inside a Virtual Machine
-----------------------------------------------------------

If you want to use the built-in web server from inside a virtual machine and then load the site
from a browser on your host machine, you'll need to listen on the `127.0.0.1` address:

.. code-block:: bash

    $ php app/console server:run 127.0.0.1:8000
```