add README.md for sequence directory
add README.md for sequence directory

DawnEve/bio_scripts,shenwei356/bio_scripts,DawnEve/bio_scripts,zctea/bio_scripts,zctea/bio_scripts,zctea/bio_scripts,shenwei356/bio_scripts,zctea/bio_scripts,shenwei356/bio_scripts,DawnEve/bio_scripts,DawnEve/bio_scripts,shenwei356/bio_scripts,zctea/bio_scripts,DawnEve/bio_scripts