doc: added commit conventions to contribution guidelines

[paumr]

This PR is a result of https://github.com/linux-nvme/nvme-cli/pull/2525#issuecomment-2394228985

Hopefully this prevents such additional workload for the maintainers in the future.

[paumr]

Just for clarification: gpg-signing the commits is a non-requirement right?

[igaw]

Excellent docs update! I was about to write something similar! Thanks!

No, gpg signing is not a requirement. I usually review everything based on what github is giving me. So the gpg signing is likely not going to help as far I understand. But I am a pretty ignorant when it comes to security.

[paumr]

Thanks! Happy to help!