create dev info page, create content for docs folder and render it

[rerpha]

We should

1. write some documentation for how to write tests, useful resources on nextjs/react/tailwind etc.
2. use something like https://markdoc.dev/docs/nextjs to generate html from the markdown files
3. render it by having a "developer" page, possibly linked to by the footer, which has a link to the wall display and the documentation.

[rerpha]

maybe we don't even need markdoc: https://nextjs.org/docs/app/building-your-application/configuring/mdx