Auto-generate index to navigate all p5js projects

[jonfroehlich]

A simpler version of #2 (which suggests making a thumbnail gallery of all projects).

Discussion on stackoverflow making a simple Python-based site generator:
https://stackoverflow.com/questions/39048654/how-to-enable-directory-indexing-on-github-pages

[jonfroehlich]

There is a Github way to do this using Jekyll but then files need to be .md: https://cl.mt/blog/github-pages-indexing-directory

Hmm.