Adding instructions for vagrant-berkshelf requirement.

The project moved from submodules to Berkshelf for the inclusion of chef cookbooks. This plugin is required for Vagrant to execute this new method.
Added NFS support commented out by default.
Removed docroot handling
Merge pull request #35 from rickmanelius/vagrant-bershelf-instructions

Adding instructions for vagrant-berkshelf requirement.
Updated readme with small link to wiki about NFS
Merge pull request #42 from timodwhit/NFS

NFS handling