JOSS request: nbsphinx and rtd

[bnord]

add the example notebooks to the RTD site via nbsphinx and nbsphinx_link -- this is a good alternative to more extensive documentation (though I would still suggest having your preferred installation instructions listed there, too)

[bnord]

Derived from #241

[bnord]

https://nbsphinx.readthedocs.io/_/downloads/en/latest/pdf/
https://github.com/readthedocs-examples/example-sphinx-basic
https://rtd-with-docsearch.readthedocs.io/en/latest/guides/jupyter.html