Document Cloudflare/GitHub Pages deploy by action

[StevenClontz]

I'm also interested in adding support for Cloudflare Pages, where every push to a repository could be built and deployed to a preview URL, with merges to main going to the canonical URL. https://developers.cloudflare.com/pages/configuration/preview-deployments/

Originally posted by @StevenClontz in #725 (comment)

[StevenClontz]

https://developers.cloudflare.com/pages/framework-guides/deploy-anything/

[StevenClontz]

Experimenting at https://github.com/StevenClontz/cloudflare-pretext-test

[StevenClontz]

A basic build was possible, but we'll want to build using our GitHub Action (to have a full devcontainer for full builds). Following https://developers.cloudflare.com/pages/how-to/use-direct-upload-with-continuous-integration/#use-github-actions to try this now.

[StevenClontz]

Demo in production at TeamBasedInquiryLearning/precalculus#341

[StevenClontz]

Implemented at #746 but we need to add documentation so folks know how to set up their GitHub repos to use it.