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.
@wcluijt Do they also provide `trusty32` and `trusty64` packages? The thing is, many people will probably have the need to use a version that is very similar to their server's version and Ubuntu 12.04 ships with PHP 5.3. If they also provide boxes for Ubuntu 14.04, we could set them here and add a comment explaining that you can also use the older Precise boxes if you need PHP 5.3.