Update documentation according to JOSS paper

[titipata]

• Adding requirements for building documentation
• Adding bits of information about scikit-learn's compatibility

[codecov-io]

Codecov Report

Merging #365 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #365   +/-   ##
=======================================
  Coverage   75.66%   75.66%           
=======================================
  Files           4        4           
  Lines         678      678           
  Branches      149      149           
=======================================
  Hits          513      513           
  Misses        128      128           
  Partials       37       37

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[jasmainak]

Thanks @titipata !