code: func NewRootNode(
  	fs billy.Filesystem,
  	submodules map[string]plumbing.Hash,
  ) noder.Noder {
  	return &node{fs: fs, submodules: submodules, isDir: true}
  }
docs: // NewRootNode returns the root node based on a given billy.Filesystem.
  //
  // In order to provide the submodule hash status, a map[string]plumbing.Hash
  // should be provided where the key is the path of the submodule and the commit
  // of the submodule HEAD