If your app depends on postgres, the current habits to state in the readme you have to install it and setup it yourself.

That's not packaging.

Goog packaging deals with that for you.

I’m not sure I follow… If you write an application in Java/Javascript/Python/C/C#/C++/Racket/Common Lisp, isn’t it the same story there? I.e. that you’re expected to provide the DB yourself.

If one desires a convenient solution there’s always Firebase, DynamoDB or even hosted PostgreSQL solutions.

For local development one can spin up a Docker image for the DBMS.

Yes, that's why packaging is more complicated as soon as you use more than your own language.

Go solves only one problem, albeit very well.