Is your feature request related to a problem? Please describe.

The generally useful guides CONTRIBUTING.md and github_guide.md still lack hints how to properly submit a pull request (PR) with reasonable title and description.

Describe the solution you'd like

Add to these guides:

• a recommendation how to write a good PR title which is explanative and also accepted by https://github.com/OSGeo/grass/blob/main/.github/workflows/titles.yml
• explanations on the PR content: which problem will be solved, is there a test, etc.

Additional context

There is currently a new PR in https://github.com/OSGeo/grass-addons/pulls written by a first-time contributor who could benefit from such guidance.