 add contributors to README
 add contributors to README

CocaColaCat/carrierwave-qiniu,weizhiwu/carrierwave-qiniu,huobazi/carrierwave-qiniu,GaiaMagic/carrierwave-qiniu,anehing/carrierwave-qiniu,huobazi/carrierwave-qiniu,lazing/carrierwave-qiniu