Add small documentation page

[visualdenniss]

https://www.pychess.org/api
build a small, minimalist and modern looking api documentation page.

Few reference examples :
https://lichess.org/api
https://nextjs.org/docs
https://vercel.com/docs

[gbtami]

I find https://github.com/hh-h/aiohttp-swagger3
Maybe it can be useful if we add the needed data inside doc strings