fix: explain code quality checks in contribution guide

[degenaro]

Types of changes

• Hot fix (emergency fix and release)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation (change which affects the documentation site)
• Breaking change (fix or feature that would cause existing functionality to change)
• Release (develop -> main)

Quality assurance (all should be covered).

• My code follows the code style of this project.
• Documentation for my change is up to date?
• My PR meets testing requirements.
• All new and existing tests passed.
• All commits are signed-off.

Summary

Key links:

• Sonar coverage

Before you merge

• Ensure it is a 'squash commit' if not a release.
• Ensure CI is currently passing
• Check sonar. If you are working for a fork a maintainer will reach out, if required.

[degenaro]

Fixes #1747.

[jpower432]

LGTM