Add function header to SynthSeg/dcan/img_processing/correct_chirality.py (from code review 2022-06-22)

[GregConan]

• Function header should explain the correct_chirality function's inputs and outputs
• One option is to copy-paste (part of) the correct_chirality function header from CABINET/src/utilities.py:

    """
    Creates an output file with chirality corrections fixed.
    :param nifti_input_file_path: String, path to a segmentation file with possible chirality problems
    :param segment_lookup_table: String, path to a FreeSurfer-style look-up table
    :param left_right_mask_nifti_file: String, path to a mask file that distinguishes between left and right
    :param nifti_output_file_path: String, path to location to write the corrected file
    """