fix help in imread (#12420)
fix help in imread (#12420)

fix help in imread
mbaijal/incubator-mxnet,mbaijal/incubator-mxnet,yajiedesign/mxnet,sxjscience/mxnet,larroy/mxnet,dmlc/mxnet,leezu/mxnet,ForkedReposBak/mxnet,ForkedReposBak/mxnet,reminisce/mxnet,apache/incubator-mxnet,mbaijal/incubator-mxnet,dmlc/mxnet,zhreshold/mxnet,zhreshold/mxnet,eric-haibin-lin/mxnet,yajiedesign/mxnet,tlby/mxnet,tlby/mxnet,szha/mxnet,sxjscience/mxnet,mbaijal/incubator-mxnet,leezu/mxnet,sxjscience/mxnet,yajiedesign/mxnet,ptrendx/mxnet,sxjscience/mxnet,reminisce/mxnet,apache/incubator-mxnet,yajiedesign/mxnet,ptrendx/mxnet,DickJC123/mxnet,ForkedReposBak/mxnet,larroy/mxnet,larroy/mxnet,szha/mxnet,leezu/mxnet,reminisce/mxnet,szha/mxnet,leezu/mxnet,zhreshold/mxnet,zhreshold/mxnet,yajiedesign/mxnet,reminisce/mxnet,eric-haibin-lin/mxnet,tlby/mxnet,tlby/mxnet,reminisce/mxnet,yajiedesign/mxnet,ptrendx/mxnet,tlby/mxnet,reminisce/mxnet,DickJC123/mxnet,larroy/mxnet,tlby/mxnet,leezu/mxnet,reminisce/mxnet,dmlc/mxnet,tlby/mxnet,mbaijal/incubator-mxnet,zhreshold/mxnet,dmlc/mxnet,eric-haibin-lin/mxnet,ForkedReposBak/mxnet,larroy/mxnet,sxjscience/mxnet,tlby/mxnet,dmlc/mxnet,zhreshold/mxnet,larroy/mxnet,zhreshold/mxnet,zhreshold/mxnet,reminisce/mxnet,dmlc/mxnet,sxjscience/mxnet,mbaijal/incubator-mxnet,apache/incubator-mxnet,ptrendx/mxnet,reminisce/mxnet,larroy/mxnet,leezu/mxnet,szha/mxnet,dmlc/mxnet,mbaijal/incubator-mxnet,eric-haibin-lin/mxnet,ptrendx/mxnet,zhreshold/mxnet,leezu/mxnet,larroy/mxnet,yajiedesign/mxnet,eric-haibin-lin/mxnet,ForkedReposBak/mxnet,szha/mxnet,ForkedReposBak/mxnet,DickJC123/mxnet,mbaijal/incubator-mxnet,ptrendx/mxnet,tlby/mxnet,szha/mxnet,sxjscience/mxnet,yajiedesign/mxnet,eric-haibin-lin/mxnet,reminisce/mxnet,dmlc/mxnet,eric-haibin-lin/mxnet,mbaijal/incubator-mxnet,leezu/mxnet,dmlc/mxnet,tlby/mxnet,szha/mxnet,szha/mxnet,eric-haibin-lin/mxnet,eric-haibin-lin/mxnet,ForkedReposBak/mxnet,ForkedReposBak/mxnet,larroy/mxnet,szha/mxnet,ptrendx/mxnet,leezu/mxnet,apache/incubator-mxnet,ptrendx/mxnet,DickJC123/mxnet,sxjscience/mxnet,ptrendx/mxnet,yajiedesign/mxnet,ForkedReposBak/mxnet,sxjscience/mxnet,ptrendx/mxnet