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