Improve the "Making Good PRs" section

I often see PRs with misleading or vague titles. This is problematic, as the PR titles often end up being the commit titles, and commit titles are one of the most important tools we have when searching for historic changes. Bad titles impact maintainability.

Suggested edits:

• Enforce a strict title format
• Promote writing accurate and concise PR titles/descriptions

Perhaps the "Making Good PRs" section can be further promoted. Would it make sense to extract it and move it a level up in the doc hierarchy?

まず開発者ガイドで「Making Good PRs」セクションを見つけ、その周辺のドキュメント階層を確認します。そのセクションで、正確かつ簡潔な pull request のタイトルと説明をどのように扱うべきか、また、より上位のレベルに置くべきかを判断します。ガイダンスと配置が issue で提案された改善を明確に反映していれば完了です。