def heading(section, guidance=""):
    """
    Add a section heading and optionally some additional guidance for 
    how to interpret the section.

    inputs
    ------
    section : (str) the title of the section
    guidance : (str) guidance to be added in italics after the section heading
                default : ""

    outputs
    -------
    head_str : (str) formatted section heading and guidance
    """

    head_str = "\section{" + section + "}\n\n"
    if len(guidance) > 0:
        head_str += "\emph{(" + guidance + ")}\n\n "

    return head_str