As a site owner the main thing you should do about .well-known is be aware that it's special and so e.g. if you add a feature where users get a vanity page at www.example.com/username you shouldn't let them have the username .well-known

The leading dot is there both because that is already special in POSIX and because there's a good chance your validation whitelisting already forbids leading dots, just like newlines, slashes and other characters we can expect to cause mayhem. So this was a less dangerous choice than just well-known without the dot.