Add guide on how to contribute Community Verified boards to the hardware catalog

[beriberikix]

https://docs.golioth.io/hardware#community-verified-boards

We'd like to encourage the community and partners to enhance our catalog by verifying the various boards supported by Zephyr. To enable that, we need to document thee process and expectations for submitting new verified boards. For now we should focus on Community Verified boards.

As in example, we may ask for a known working overlay, sample and a pointer to a repo with the details, though we probably want to be more detailed.