docs(minimal reproductions): add perfect example

[HonkingGoose]

Changes

• Add example of a perfect reproduction: renovate-reproductions/12260 repository
• Improve the "Create readme.md instruction:
  • Ask readers to use headings to organize the information
  • Ask readers to add a link to the upstream Renovate Issue or Discussion

Context

@rarkins suggested showing examples of perfect reproductions. I think one of my reproductions is a perfect example, so I'm adding it to the docs. 🙃

Helps with a part of this discussion:

• Minimal reproduction instructions/templates #28614

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 37.382.3 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 37.382.3

Your semantic-release bot 📦🚀