I wrote the README and also fixed a minor performance bug.

Because Prism code editor only initializes once Svelte finishes hydrating, there’s a delay of a few hundred milliseconds between when the page becomes visible and when the editor initializes. This caused a layout shift on each puzzle page, which was making Lighthouse take away a few points in the performance category. So I precalculated the height of each puzzle editor in advance and applied that minimum height to the placeholder text. This fixed the layout shift, so now Lighthouse gives the site perfect 100s in performance, best practices, and SEO, which is cool.