Add the header to the CSV file

def write_header(fobj):
    """Add the header to the CSV file"""
    fobj.write("# K40 calibration results\n")
    fobj.write("det_id\trun_id\tdom_id")
    for param in ['t0', 'qe']:
        for i in range(31):
            fobj.write("\t{}_ch{}".format(param, i))