Update CONTRIBUTING.md with coding standards and best practices

[trunk-io[bot]]

⏱️ 12m total CI duration on this PR

Job	Cumulative Duration	Recent Runs
tests (HEAD)	12m	🟩 🟩
check-changelog	6s	🟩 🟩

_{settings ⋅ feedback ⋅ docs ⋅ learn more about trunk.io}

[dermatz]

@Morgy93 any news about this PR?

[Morgy93]

@Morgy93 any news about this PR?

There's one open conversation that needs to be resolved: https://github.com/dermatz/ddev-woodoo-buildtools-magento/pull/49#discussion_r1728435592