added spinix.ext.napoleon to sphinx extensions

[abrown41]

I recently used this cookie cutter template having seen it in action at the SeptemRSE conference. I then spent three weeks trying to make sphinx work with my code (I have never used sphinx before). It turned out a particular doc-string in pandas.core.frame doesn't play nicely with numpydoc unless you have the sphinx.ext.napoleon extension enabled.

Given that a lot of scientific python projects will probably use pandas DataFrames, and that many of the people you want to use this cookie cutter template may not have used sphinx before, this PR adds the extension to the list in docs/source/conf.py to save them the pain.

[bielsnohr]

Thanks for the contribution @abrown41 and sorry for taking so long to reply. For some reason the notification didn't come through to me by email.

It is great to get feedback from those using the template. This sounds like a very sensible change, but I will just need to quickly test it before agreeing to merge in. I don't imagine it will cause any trouble.

[bielsnohr]

After a lot of struggling, I discovered that having both numpydoc and sphinx.ext.napoleon seems to cause the very basic example used for testing to fail. It runs fine if only one or the other is enabled. The error if both are enabled:

Warning, treated as error:
/home/mbluteau/work/projects/scientific-python-cookiecutter/example/docs/source/autoapi/example/_version/index.rst:179:Explicit markup ends without a blank line; unexpected unindent.

@abrown41 Did you come across this? By the looks of this PR you have both enabled, which is surprising.

Given that napoleon can handle both Google style and numpy style docstrings, I am inclined to use it instead of numpydoc, but I will wait to hear back.

[bielsnohr]

As mentioned in previous comments, this suggestion to use napoleon seems sensible, although it appears from testing that numpydoc should not be used at the same time, so I have suggested it be removed.