DOC: add missing docs - #12250

Good idea to clean this up. A few comments:

• It looks to me like the distutils guide should go into the user guide, not the reference docs.
• C style guide should either become a NEP or be part of the dev guide, not the reference docs.
• The distutils section could also use a few simple cleanups, it's clear now that it was written 10 years ago: change references to "SciPy" to general scientific packages, edit the "useful functions ..." section and turn things into links there.

Additionally, the conduct/report_handling_manual.rst and alignment.rst documents were not linked into a TOC, thus unavailable via links.

That's not quite how it works, e.g. the report_handling page is linked from https://www.numpy.org/devdocs/dev/conduct/code_of_conduct.html#incident-reporting-resolution-code-of-conduct-enforcement. I'll comment on these changes separately.

The top level CAPI.rst.txt is not linked in, I think we can drop or move it to informational NEPS if it has historical relevance still.

That sounds right. Would be good to verify that all content is already present in the docs - did you do that?

I broke these::

- It looks to me like the distutils guide should 
  go into the user guide, not the reference docs.
- C style guide should either become a NEP or be 
  part of the dev guide, not the reference docs.
- The distutils section could also use a few simple
  cleanups, it's clear now that it was written 10 years ago: 
  - change references to "SciPy" to general scientific packages
  - edit the "useful functions ..." section and turn things into links there.

out into a separate issue #12261

Changesets aeefb51 and 00e8e16 refactored and removed the outdated CAPI.rst.txt, after merging relevant information back into the docs

C style guide should either become a NEP or be part of the dev guide, not the reference docs.

Moved to dev section

@rgommers ping

Okay, in it goes. Thanks @mattip