allow adding packages without a path

[davidnewhall]

In CI the path does not contain GitHub.com or the org name, so allowing adding packages with an absolute path separate from the name.

Example:

	localPrefix    = "github.com/Notifiarr/notifiarr/"

	for _, pkg := range localPkgs {
		dir := strings.TrimPrefix(pkg, localPrefix)
		docs.AddPkgMust(path.Join("../../../", dir), pkg) // `git clone`
	}