I actually think njump.me 's text is pretty good, of something isn't make specifically. You could screenshot and print. Just an idea.
It is good. But too long for a flyer. And the dynamic title wont work. It would also be nice for people to know that nostr already has hundreds of applications and thousands of relays and is growing fast... that it is the next big thing... that it is totally open and free and not tied to any company. Because I think people will assume it is a product or a centralized thing or maybe some small idea that hasn't proven itself yet.... those wrong assumptions people make generally cause people to dismiss it before the recognize it for what it is.
Yeah hopefully someone comes up with something appropriate. I think something flyer length with the main points that you said (I would also add the ability to build on it as a key feature), would also be super useful as a website too. There's a few 'what is nostr' type sites but they mostly ramble on a bit. Could have a more succinct bit of text/images and links to more info/advanced.