Custom facts should be supported

[trevor-vaughan]

Use Case

strings covers almost the entire Puppet module ecosystem with the exception of custom facts. I would like strings to be able to generate documentation for custom facts so that I do not need to reproduce the content by hand.

I understand that some facts are complex but even just noting which ones need to be seen in the README and auto-documenting the rest would be a huge benefit.

Describe the Solution You Would Like

A Custom Facts section is present in the REFERENCE.md