Rework the docs for NEWS/What's New entries

[erlend-aasland]

• Add subsubsections instead of keeping all the text in a single large subsection
• Add some text about how to word NEWS entries
• Mention that test and strictly internal changes seldom require NEWS entries

(Some minor wording changes might have snuck in, but largely, I kept the existing text.)

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📚 Documentation preview 📚: https://cpython-devguide--1238.org.readthedocs.build/core-developers/committing/#updating-news-and-what-s-new-in-python

[AlexWaygood]

Thanks, this is great! I agree that https://github.com/python/devguide/pull/1238/files#r1417449912 would improve things further.

Also: should we think about moving this information to a different file altogether? This information isn't just relevant to core developers; it's relevant to any contributors.

It's possible (and easy) for core developers to add NEWS entries to other contributors' PRs, but few core devs do so; the de-facto expectation is that contributors should write their own NEWS entries

[erlend-aasland]

Also: should we think about moving this information to a different file altogether? This information isn't just relevant to core developers; it's relevant to any contributors.

That's a good idea. Let's do it in a follow-up PR.

[erlend-aasland]

I'm very pleased with how this turned out. Thanks for your input, everyone! I'll land tomorrow.

[erlend-aasland]

@AlexWaygood and @ezio-melotti, I've created follow-up issues for your suggestions regarding further improvements. Let me know if I forgot something.

• Consider relocating NEWS/What's New docs #1242
• Add more examples to the NEWS/What's New docs #1243