New docs!

[arlyon]

I took some time to write some documentation. It could do with some work, probably, but it's a start. Please leave feedback here.

https://www.payments.rs/docs
https://www.payments.rs/llms-full.txt

[Firgrep]

Looks very nice! Appreciate the contributing guidelines 🎈

[arlyon]

I have tried to de-duplicate files where possible (direct snippets from source code, including the 'normal' md files as symlinks) so hopefully we won't get too much drift.