setto on Nostr: In your webroot, you create a folder called `.well-known` and inside of that a file ...

In your webroot, you create a folder called `.well-known` and inside of that a file called `nostr.json`. Here's how ours at Dyne.org look:
https://github.com/dyne/dyne.github.io/blob/main/public/.well-known/nostr.json

The npun needs to be in its hexiadecimal version.