Add Attribute examples and descriptions to the policyfile documents

[snohio]

Is your feature request related to a problem? Please describe.

The customer World Bank (among others) would like to have examples and descriptions of how to utilize attributes in the policyfiles so that they can understand how they work.

Describe the solution you'd like

Include examples and descriptions of Attributes in the https://docs.chef.io/config_rb_policyfile/ and https://docs.chef.io/policyfile/ documents.

Describe alternatives you've considered

The alternative is that the SA and CA teams continue to hold peoples hands when they ask how to do this.

Additional context

None needed.