Fix README flags

[schorlton]

The new flags in the README are incorrect. I've simply updated them to match:

Porechop/porechop/porechop.py

Lines 187 to 211 in cc40f6f

	main_group.add_argument('--barcode_stats_csv', action='store_true',
	help='Option to output a csv file with start/ end/ middle barcode names '
	'and percentage identities for each given read. ')
	main_group.add_argument('--format', choices=['auto', 'fasta', 'fastq', 'fasta.gz', 'fastq.gz'],
	default='auto',
	help='Output format for the reads - if auto, the '
	'format will be chosen based on the output filename or the input '
	'read format')
	main_group.add_argument('-v', '--verbosity', type=int, default=1,
	help='Level of progress information: 0 = none, 1 = some, 2 = lots, '
	'3 = full - output will go to stdout if reads are saved to '
	'a file and stderr if reads are printed to stdout')
	main_group.add_argument('-t', '--threads', type=int, default=default_threads,
	help='Number of threads to use for adapter alignment')
	barcode_group = parser.add_argument_group('Barcode binning settings',
	'Control the binning of reads based on barcodes '
	'(i.e. barcode demultiplexing)')
	barcode_group.add_argument('-b', '--barcode_dir',
	help='Reads will be binned based on their barcode and saved to '
	'separate files in this directory (incompatible with '
	'--output)')
	barcode_group.add_argument('--barcode_labels', action='store_true',
	help='Reads will have a label added to their header with their barcode')
	barcode_group.add_argument('--extended_labels', action='store_true',