How to "Add Markdown Content" to OpenAPI content?

Hello,

I am interested in the following feature, but it's not clear to me how to actually do this:
https://docs.readme.com/main/docs/openapi#adding-markdown-content

Can anyone point me to instructions for how to actually accomplish this?

Please note that we manage all of our content in a GitHub repo and use the CLI to import both markdown files and the OpenAPI JSONs, so I'd need to know the flow for how to use this feature given our constraints.

Thank you all for your time!