Documents parameter-less (base!) case

Per https://github.com/opscode/chef/blob/dd742991862f6b1c9b8d193549f6b87c5c92cfa6/spec/unit/resource_definition_spec.rb and my own testing, this document now reflects reality. Definitions do not require parameters and can therefore be used as simple parameter-less macros.
Merge pull request #359 from jblaine/patch-5

Documents parameter-less (base!) case