Added Vagrant configuration cookbook

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | n/a

A new cookbook article was added with an example Vagrant configuration that can be used with the Symfony Standard Edition.
I think at some point when I was writing this cookbook, I thought about mentioning how a developer could edit their `/etc/hosts` file so that they could access their development site from `www.symfony.local`, but it was just extra information and someone might get stuck there when they are practically done.  It was much easier to just go directly to the IP address that was already available right now.