Extends an ArgumentParser instance with the following commandline arguments:
        --context-size

def add_reference_context_args(parser):
    """
    Extends an ArgumentParser instance with the following commandline arguments:
        --context-size
    """
    reference_context_group = parser.add_argument_group("Reference Transcripts")
    parser.add_argument(
        "--context-size",
        default=CDNA_CONTEXT_SIZE,
        type=int)
    return reference_context_group