[REQ] Add a markdown generator

Created by: alexander-matthiesen

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

Currently we are trying to convert our OpenAPI-Specification into a markdown format that we can use this generated markdown in mkdocs.

Describe the solution you'd like

I would like to have a generator that converts oas2 and oas3 files to .md files

Describe alternatives you've considered

I tried swagger2md or even converting the oas2 file to a wiki book and from that to markdown, but nothing was satisfying.

Additional context

I've seen that there is a html-markdown script in this repository, but I couldn't get it running. Some help would be nice.