[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 | 
I like a sidebar.

We should have someone try this - I don't have a VM handy (and my laptop's meager HD is too small to run one), but I *think* I remember `127.0.0.1` working with VirtualBox.