docs: comprehensive codebase documentation (long-term goal)

[xynydev]

The README should include documentation on things such as how the project is structured, which files contain important bits, and how to get started with local development.

Additionally, as this project is a big part of the BlueBuild build chain, higher level documentation should be written and possible diagrams made to help us manage and new contributors or learners to understand also the bigger picture through the fundamental building blocks of the system.

This higher-level documentation would probably live on the website, but that is to be discussed, and some effort from the cli team would be required.

This is less important than more user-facing documentation, and should only be done after a stable API is established. I would of course help with writing and designing the documentation. I'm also planning to delve into the codebase a bit with some type of contribution, so we'll see.