Document an easy way to get current number of consumed nodes.

[vinyar]

The functionality is out there, but it doesnt seem to be documented.
Not sure on the place place, perhaps start with here:
https://docs.chef.io/chef_license.html
and
https://docs.chef.io/api_chef_server.html

knife raw license -s https://localhost/ -c /etc/opscode/pivotal.rb

# knife raw license -s https://localhost/ -c /etc/opscode/pivotal.rb
{
  "limit_exceeded": true,
  "node_license": 25,
  "node_count": 28124,
  "upgrade_url": "http://www.getchef.com/contact/on-premises-simple"
}