It's not only that the documentation is quite bad. It's also the rest of go.

Here's what it spews when you specidy a dependency incorrectly

Dependency:

  github.com/robfig/cron v3.0.1

go's handling of this:

  require github.com/robfig/cron: version "v3.0.1" invalid: 
  module contains a go.mod file, so major version must be 
  compatible: should be v0 or v1, not v3

Right. What?

I solved it by looking through this issue that comes at the top of Google Search for it: https://github.com/golang/go/issues/35732