Here's nvm for comparison :

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.1/install.sh | bash

I would go for that as a standard to aim for @cel. Things I like about that :

• it's at a URL which I can read as a human
• I have opened that file to see what sorts stuff it has in it
• it's not too long (which gets scary)

I would consider making a route like :

http://installers.scuttlebot.io/git-ssb/v1.3.12/install.sh

You're running a server, this can just map to whatever blob, but it looks and feels legit. The good thing is that tag could map to a git tag. There's not reason for advanced users you can't have whatever else as well, like localhost, but TBH I think localhost doesn't really help people trying to bootstrap in if they're not in proximity to you the developer.