Try cleaning up the CONTRIBUTING.md/developer_notes.rst dichotomy

https://github.com/pyvista/pyvista/pull/2104 made me realise that we have two files with almost the same contents: CONTRIBUTING.md and doc/extras/developer_notes.rst.

It seems to me that the two files should have the same contents (other than the obvious markup differences), but they have diverged a bit over time. Now care must be taken to change anything in them in unison, otherwise the distance increases between the two.

So my question is: can we do something about this? Is there some way that we can generate either file from the other? Something like pypandoc perhaps, if our existing tooling can’t do this? It seems like needless repetition and maintenance overhead that would be great to get rid of. Since CONTRIBUTING.md is a standard file, the ideal direction would be to generate doc/extras/developer_notes.rst from the former. From a quick glance it seems that all links are either completely external (i.e. fully qualified URLs) or internal to the same file. This should make this more feasible.

[tkoyama010]

@adeak Thank you for pointing out this. I thought the same thing and made https://github.com/pyvista/pyvista/pull/2110.

[banesullivan]

We could change CONTRIBUTING.md to be re-structured text (.rst) and then include its contents in doc/extras/developer_notes.rst when building the docs.