Creates a sequence of child nodes for the given list of moves.
        Adds *comment* and *nags* to the last node of the line and returns it.

def add_line(self, moves: Iterable[chess.Move], *, comment: str = "", starting_comment: str = "", nags: Iterable[int] = ()) -> "GameNode":
        """
        Creates a sequence of child nodes for the given list of moves.
        Adds *comment* and *nags* to the last node of the line and returns it.
        """
        node = self

        # Add line.
        for move in moves:
            node = node.add_variation(move, starting_comment=starting_comment)
            starting_comment = ""

        # Merge comment and NAGs.
        if node.comment:
            node.comment += " " + comment
        else:
            node.comment = comment

        node.nags.update(nags)

        return node