Expand docs to MkDocs deployment

[HumbleDeer]

Intent

This expands the current docs to be an MkDocs deployment.

Deployment

Deploying this requires enabling GitHub Pages, and activating deployment from a GitHub Actions workflow:

1. https://docs.github.com/en/pages/getting-started-with-github-pages/creating-a-github-pages-site (follow only steps to enable Pages)
2. Deploy from Action:https://docs.github.com/en/pages/getting-started-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site#publishing-with-a-custom-github-actions-workflow

The deployment will live at https://armchairengineeri.ng/Xol-Toolhead (analogous to https://Armchair-Engineering.githhub.io/Xol-Toolhead).