Consider / plan a conversion to Gatsby (with `spec-md` as a plugin?)

Follows-up on #6

Netlify and Gatsby is the predominant way we build sites at Apollo. While it has some shortcomings, our team is familiar with it and we should build on that (and have them fix the short-comings). That said, I find `spec-md` to be pretty great for what we're trying to represent here.

Strawdog/needs-full-plan: I think rather than generating the `spec-md` HTML via CLI, we could instead use [its API](https://spec-md.com/#sec-Using-Spec-Markdown)'s `html` method, perhaps coupled with a Gatsby source plugin [like, but maybe not `gatsby-source-plugin`](https://www.gatsbyjs.com/plugins/gatsby-source-filesystem/) and a subsequent transformer.

Start by reviewing the follow-up issue #6 and the spec-md API documentation linked in the issue, especially its html method. Evaluate the proposed Gatsby source-plugin and transformer approach against the current CLI-generated HTML workflow. Done means a documented, agreed full plan for the conversion, including how Netlify and spec-md fit into it.

Written by the indexing model from the issue text.