def check_requirement(line):
    """
    Check this line for a requirement, which is indicated by a line betinning with "?? ".
    If one is found, return that line with a newline at the end, as requirements are always
    a complete line and formatted as a bulleted list.  Replace the "??" with a "-" as well
    so that the resulting list can later be Markdown formatted.
    :param line: the line to check
    :return: None or a formatted requirement
    """
    if line[0:3] == "?? ":
        return "- %s\n" % line[3:]
    return None