Create a rustbook user/developer documentation

[kirillbobyrev]

• [ ] Create a rustbook with documentation
• [ ] Push it to GitHub Pages

Would be nice to move Developer and User documentation there, as well as some experiment logs/other useful info. Good candidates are:

• [ ] Code map (an extension of what currently resides in README) and pointers (Rustdoc-generated documentation, etc)
• [ ] Instructions on building
• [ ] Development workflow: changing the code, testing (unit, integration, SPRT), fuzzing and benchmarking it and preparing a patch
• [ ] Different recipes (just lint, just fmt and so on) for development
• [ ] Supported features (UCI, implementation features)
• [ ] NNUE training process and recipes