doc: reflect new usage
doc: reflect new usage

jacobtomlinson/multer,kangkot/multer,expressjs/multer,jg3526/multer,kylev/multer,ACT1GMR/multer,zhaoshiling1017/multer,wowzzangga/multer,ramanujadasu/multer,hwqin/multer,xixilive/multer,tchungdojo/multer,mixxen/multer