I don’t speak for Fly, as I’m just a customer, but the odds of Fly launching any conceivable project on GitHub as an official offering is, I’d guess, pretty low. I’d say just follow the instructions in that guide; a TOML configuration file is already provided for you.
The one worry I’d have is that the config looks like it’ll start up a single instance. You might want to see if the server supports clustering and self-healing before you start storing valuable data in it; we’ve had a few folks running single-cluster databases here, despite the recommendation against it, and they’ve gotten annoyed when the underlying hardware has failed.