private function findSubPackages(PackageInterface $package): Generator
    {
        $readMes = new \Symfony\Component\Finder\Finder();
        $readMes->files()
                ->in($package->getPaths())
                ->depth(1)
                ->name('readme.md');

        // If no sub-folders have a readme, there aren't any sub-packages here.
        if (!$readMes->count()) {
            return;
        }
        yield from $this->scanNamespaceForPackages($package, $package);
    }