GH-931: Improve "Making Good PRs" docs with title guidelines and structure

[Austin-John]

Improve the "Making Good PRs" section

• Adds explicit rules for PR titles (imperative verbs, GH-issue references).
• Includes a PR submission checklist and examples of good/bad titles.

Fixes GH-931

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📚 Documentation preview 📚: https://cpython-devguide--1521.org.readthedocs.build/

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[hugovk]

Did you check the output of this?

Did you use ChatGPT for this? Please see our policy on generative AI: https://devguide.python.org/getting-started/generative-ai/

And remember to sign the CLA.

[hugovk]

Actually, these changes have been made to wrong file. The contrib/ files are a work in progress, see the (important) text you deleted.

[Austin-John]

Hi @hugovk,
Thank you for reviewing my PR and for the opportunity to contribute! I understand that someone else had already addressed the issue, and I’m glad it’s resolved now.

This was my first time contributing to an open-source project, and I learned a lot in the process. I’m excited to continue contributing. If you have any advice on how I can get more involved in open source or improve my contributions, I’d really appreciate it!

Best regards