Add CLI output explaining how to add yourself to the list

Saw a great recommendation from @iarna on the package.community Discord channel which I just joined.

> Decentralized contribution info or no, I'd like npx thanks to point folks where to learn about how to add themselves. So it's less of a "cool kids" thing

Totally agree. I was planning to add this but forgot to do it.

Start by locating the entry point for the `npx thanks` CLI and review how its current output is assembled. Add guidance that tells people how to add themselves to the list, then run the CLI and verify that the explanation appears clearly in its output.

Written by the indexing model from the issue text.