[hint compat] Add architeture documentation

[molant]

📚 Docs improvements

The compat-api hint is pretty big and complex. We need to document how it works, ideally with some diagrams and such, in an architecture.md file to make sure we don't forget how it works in a couple months.

[bruiztorres]

About the documentation I’m not 100% sure about what kind of diagrams you are expecting. Could you check this diagram and let me know your feedback?

[molant]

This diagram looks good. I think that we will need more detail in the documentation with examples of Error refinement, quirks, etc.

@antross anything else you can think of?