I generally like your changes to the README a lot, but the requirements section typically lists the required version of Chef, cookbook dependencies, and supported OS versions. This is another Chef convention, see https://github.com/opscode-cookbooks/mysql#requirements or any of the external cookbooks I've linked to.

The requirements you've moved up here are in fact the requirements of using the cookbook with Vagrant and not the requirements of the cookbook itself. Remember that the cookbook can already be used under many different environments (Vagrants, EC2, VMware, bare metal). That's the reason why I've addressed Vagrant in the Usage section.