Short docs here: https://github.com/leesalminen/lnbits-legend/blob/ad572f267a6384e2912722b79afb9afdfa24396b/lnbits/extensions/nostrnip5/README.md

Of course, would recommend you self-hosting your own LNBits instance, too. And this extension hasn’t been merged upstream yet. So, probably best to wait for it to get merged to main.

If you’re feeling reckless, create a wallet at https://lnbits.fly.dev, enable the nostr nip-5 extension, add your domain, and follow instructions in the readme link above to configure your webserver.