We should use the documentation from #206 to generate a full doc.go in cmd/librarian, so that the content shows up at https://pkg.go.dev/github.com/googleapis/librarian/cmd/librarian.

See https://pkg.go.dev/cmd/go as an example. Code is here:
https://github.com/golang/go/blob/master/src/cmd/go/internal/help/help.go

Also run go help modules as an example for the type of content.