How do you get a random site you like to join the fediverse?

Suppose there's this site I really like, and I like the fediverse, and I think it would be awesome if they joined the fediverse, to benefit everyone involved. Is it like how it was in the Zorro movie where they vote California into the US, Zorro swipes all the voting boxes with a Z, and everyone cheers, or is it not possible for just any random schmoe site to join?