"You have closed registrations on mastodon.social, so how will my friends get in or find me?"
Tell your friends to sign up on https://knzk.me/about then tell them: "Search for MyUsername@mastodon.social" and voilà, you have found each other.
It's very similar to how e-mail addresses work.
This Mastodon instance is for people interested in technology. Discussions aren't limited to technology, because tech folks shouldn't be limited to technology either!