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 believe these xdebug lines are here to ensure that Symfony (or maybe Twig?) works correctly.  Anything else could be added by the developer when they are customizing their configuration for their particular environment.  I'm not sure if newer developers will use Xdebug when they are just starting, but when they do decide they need to use Xdebug, it should be simple enough to duplicate a `file_line { ... }` section and update the `line` value.

In my own `vagrant/Vagrantfile`, I sometimes add this comment about using Xdebug with PHPStorm to remind myself:

```
# - Debugging
# To use Xdebug in the virtual machine command line with PHPStorm, go to PHPStorm > Preferences > PHP > Servers and add a new server with the following information:
# Name: vagrant, Host: 192.168.33.10, Port: 80, Debugger: Xdebug
# Check the box to enable the "Use path mappings" setting and specify the "Absolute path on the server" for the main project path as: /vagrant
# Then, use the following command in the virtual machine (via the "vagrant ssh" command):
# export XDEBUG_CONFIG="remote_host=192.168.33.1 idekey=phpstorm-xdebug" PHP_IDE_CONFIG="serverName=vagrant"
# Notice that the remote_host is set to 192.168.33.1 and not 192.168.33.10 since it is specifying the physical host IP address
# To stop debugging, use the following command in the virtual machine:
# unset XDEBUG_CONFIG PHP_IDE_CONFIG
```