Write page for "Other / Generic" support tool

[humitos]

We are promoting Sphinx, MkDocs and Jupyter Book as the only Supported tools in our main website. However, we support more tools than those ones. I propose to write a "Generic tool" page to explain this use case is also supported.

I think potential customers that are using a different doctool won't sign up if they see here that we don't support other doctools.

[agjohnson]

Noting this could be Markdoc support too, maybe a individual page eventually. Docusaurus as well

[ericholscher]

I added #336 for Markdoc and #337 for generic tool.