Adds documentation for cf-icons
Adds documentation for cf-icons

This commit directly copies the documentation on
https://cfpb.github.io/cf-icons/docs/ and converts it to our new
documentation format. Right now the icons aren't loaded when the
documentation is generated and that needs to be looked at.

cfpb/capital-framework,contolini/capital-framework,contolini/capital-framework,cfpb/capital-framework