fix for the help message called using -h

bin/footprints_extraction.py

@@ -42,7 +42,7 @@ def parse_args():
 	parser.add_argument('--output_file', default='footprints_extraction.bed', type=str, help='Please enter a name for the output file, by default ./footprints_extraction.bed.')
 	parser.add_argument('--window_length', default=200, type=int, help='Please enter the length for a window, by defauld 200 bp.')
 	parser.add_argument('--step', default=100, type=int, help='Please enter a step to move the window, by default 100 bp.')
-	parser.add_argument('--percentage',  default=0, type=int, help='Please enter a percentage to be added to background while searching for footprints, by default 0%.')
+	parser.add_argument('--percentage',  default=0, type=int, help='Please enter a percentage to be added to background while searching for footprints, by default 0%%.')
 	parser.add_argument('--silent', action='store_true', help='While working with data write the information only into ./footprints_extraction.log.')
 	args = parser.parse_args()