FR: Provide Documentation

[stellarpower]

Are there any docs available for xtensor-sparse? Guessing not currently, as it'd probably be in the readme if so!

So even a basic doxygen sort of thing would be nice to have, mirroring the main xtensor's deployment to readthedocs.io.

Thanks!!

[Roy-Kid]

Hi, what a nice work! I already use it in my project, and I also wonder if it can provide doc and vcpkg? Thx a lot!