add basic documentation via sphinx

[lukasheinrich]

[eduardo-rodrigues]

Hi folks, just browsing the outstanding issues ... let me comment on this: for a small package such as this one you could also make your life easier and provide documentation via one or two notebooks (aside quick get-started snippets in the README, which are always good for a first contact with a package). My 2 cents :-).

[eduardo-rodrigues]

What do you think of my comment above, @matthewfeickert and @lukasheinrich?