Display information about obtaining the aeidon module.

def prerequisites():
    """Display information about obtaining the aeidon module."""

    url = "http://home.gna.org/gaupol/download.html"
    debian = "sudo apt-get install python3-aeidon"
    other = "python3 setup.py --user --without-gaupol clean install"

    LOGGER.error(
        "The aeidon module is missing!\n\n"
        "Try '{0}' or the appropriate command for your package manager.\n\n"
        "You can also download the tarball for gaupol (which includes "
        "aeidon) at {1}. After downloading, unpack and run '{2}'."
        .format(debian, url, other))