Add an architecture page in the docs

[Oni-giri]

The docs regarding how to contribute are clear, however I noticed that very useful architectural explanations were included in ./llm.txt.

I guess that it would help non-vibe coders contributors. I propose to do a bit of reformatting for human consumption and add it to the documentation.

[RobinPicard]

Great idea! If you could update the content of llm.txt that would be awesome too. For the part to add to the documentation for human conception, I think it could make sense to put it in the Guide section and add a link to the page in the contribution guide.