Update documentation for mxnet.image.imdecode (#5957)
Update documentation for mxnet.image.imdecode (#5957)

* Update documentation for mxnet.image.imdecode

* Update documentation for mxnet.image.imdecode (clarify that we need OpenCV and not the CV2 Python library)

TuSimple/mxnet,jamesliu/mxnet,DR08/mxnet,reminisce/mxnet,smolix/incubator-mxnet,arikpoz/mxnet,hpi-xnor/BMXNet,Mega-DatA-Lab/mxnet,luoyetx/mxnet,ZihengJiang/mxnet,hesseltuinhof/mxnet,larroy/mxnet,ForkedReposBak/mxnet,coder-james/mxnet,kevinthesun/mxnet,luoyetx/mxnet,navrasio/mxnet,tlby/mxnet,zhreshold/mxnet,pluskid/mxnet,DR08/mxnet,saurabh3949/mxnet,Mega-DatA-Lab/mxnet,sergeykolychev/mxnet,jamesliu/mxnet,xcgoner/dist-mxnet,jiajiechen/mxnet,likelyzhao/mxnet,Mega-DatA-Lab/mxnet,DickJC123/mxnet,antoan2/incubator-mxnet,xcgoner/dist-mxnet,stefanhenneking/mxnet,larroy/mxnet,jermainewang/mxnet,kevinthesun/mxnet,TuSimple/mxnet,tornadomeet/mxnet,nicklhy/mxnet,CodingCat/mxnet,leezu/mxnet,smolix/incubator-mxnet,leezu/mxnet,ykim362/mxnet,ForkedReposBak/mxnet,zhreshold/mxnet,ShownX/incubator-mxnet,gautamkmr/incubator-mxnet,xcgoner/dist-mxnet,Ldpe2G/mxnet,jiajiechen/mxnet,jennyzhang0215/incubator-mxnet,LinkHS/incubator-mxnet,gautamkmr/incubator-mxnet,antoan2/incubator-mxnet,weleen/mxnet,crazy-cat/incubator-mxnet,smolix/incubator-mxnet,LinkHS/incubator-mxnet,solin319/incubator-mxnet,hpi-xnor/BMXNet,Northrend/mxnet,kkk669/mxnet,madjam/mxnet,CodingCat/mxnet,weleen/mxnet,Ldpe2G/mxnet,lxn2/mxnet,piiswrong/mxnet,zhreshold/mxnet,leezu/mxnet,weleen/mxnet,ForkedReposBak/mxnet,vikingMei/mxnet,navrasio/mxnet,arikpoz/mxnet,hpi-xnor/BMXNet,precedenceguo/mxnet,LinkHS/incubator-mxnet,kevinthesun/mxnet,dmlc/mxnet,saurabh3949/mxnet,precedenceguo/mxnet,DR08/mxnet,tornadomeet/mxnet,Prasad9/incubator-mxnet,saurabh3949/mxnet,jiajiechen/mxnet,TuSimple/mxnet,ForkedReposBak/mxnet,Northrend/mxnet,luoyetx/mxnet,coder-james/mxnet,kkk669/mxnet,formath/mxnet,leezu/mxnet,jamesliu/mxnet,EvanzzzZ/mxnet,kevinthesun/mxnet,szha/mxnet,thirdwing/mxnet,apaleyes/mxnet,hesseltuinhof/mxnet,LinkHS/incubator-mxnet,fullfanta/mxnet,wangyum/mxnet,szha/mxnet,leezu/mxnet,xcgoner/dist-mxnet,sergeykolychev/mxnet,LinkHS/incubator-mxnet,arikpoz/mxnet,jiajiechen/mxnet,ShownX/incubator-mxnet,antoan2/incubator-mxnet,formath/mxnet,gautamkmr/incubator-mxnet,Northrend/mxnet,Northrend/mxnet,piiswrong/mxnet,jamesliu/mxnet,sergeykolychev/mxnet,reminisce/mxnet,piiswrong/mxnet,fullfanta/mxnet,ZihengJiang/mxnet,stefanhenneking/mxnet,fullfanta/mxnet,dmlc/mxnet,ZihengJiang/mxnet,navrasio/mxnet,reminisce/mxnet,Prasad9/incubator-mxnet,crazy-cat/incubator-mxnet,stefanhenneking/mxnet,indhub/mxnet,rishita/mxnet,saurabh3949/mxnet,navrasio/mxnet,sergeykolychev/mxnet,saurabh3949/mxnet,danithaca/mxnet,mbaijal/incubator-mxnet,weleen/mxnet,likelyzhao/mxnet,coder-james/mxnet,Prasad9/incubator-mxnet,thirdwing/mxnet,arikpoz/mxnet,navrasio/mxnet,szha/mxnet,sxjscience/mxnet,thirdwing/mxnet,madjam/mxnet,ykim362/mxnet,jermainewang/mxnet,coder-james/mxnet,saurabh3949/mxnet,solin319/incubator-mxnet,Prasad9/incubator-mxnet,EvanzzzZ/mxnet,fullfanta/mxnet,tornadomeet/mxnet,xcgoner/dist-mxnet,saurabh3949/mxnet,hpi-xnor/BMXNet,ZihengJiang/mxnet,madjam/mxnet,kevinthesun/mxnet,lxn2/mxnet,vikingMei/mxnet,mbaijal/incubator-mxnet,EvanzzzZ/mxnet,ShownX/incubator-mxnet,indhub/mxnet,ykim362/mxnet,hpi-xnor/BMXNet,hotpxl/mxnet,indhub/mxnet,rahul003/mxnet,madjam/mxnet,lxn2/mxnet,jamesliu/mxnet,nicklhy/mxnet,arikpoz/mxnet,ykim362/mxnet,precedenceguo/mxnet,jennyzhang0215/incubator-mxnet,apache/incubator-mxnet,arank/mxnet,larroy/mxnet,sxjscience/mxnet,hesseltuinhof/mxnet,larroy/mxnet,stefanhenneking/mxnet,yajiedesign/mxnet,thirdwing/mxnet,tornadomeet/mxnet,hotpxl/mxnet,ptrendx/mxnet,stefanhenneking/mxnet,rishita/mxnet,leezu/mxnet,rishita/mxnet,lxn2/mxnet,yuruofeifei/mxnet,szha/mxnet,precedenceguo/mxnet,LinkHS/incubator-mxnet,indhub/mxnet,yuruofeifei/mxnet,zhreshold/mxnet,crazy-cat/incubator-mxnet,jermainewang/mxnet,vikingMei/mxnet,eric-haibin-lin/mxnet,CodingCat/mxnet,CodingCat/mxnet,wangyum/mxnet,Mega-DatA-Lab/mxnet,ykim362/mxnet,rishita/mxnet,luoyetx/mxnet,solin319/incubator-mxnet,mbaijal/incubator-mxnet,antoan2/incubator-mxnet,thirdwing/mxnet,pluskid/mxnet,Prasad9/incubator-mxnet,dmlc/mxnet,dmlc/mxnet,vikingMei/mxnet,LinkHS/incubator-mxnet,Ldpe2G/mxnet,ykim362/mxnet,mbaijal/incubator-mxnet,hesseltuinhof/mxnet,EvanzzzZ/mxnet,pluskid/mxnet,nicklhy/mxnet,xcgoner/dist-mxnet,larroy/mxnet,hotpxl/mxnet,likelyzhao/mxnet,arank/mxnet,thirdwing/mxnet,stefanhenneking/mxnet,jiajiechen/mxnet,piiswrong/mxnet,sxjscience/mxnet,eric-haibin-lin/mxnet,yajiedesign/mxnet,szha/mxnet,saurabh3949/mxnet,hpi-xnor/BMXNet,ZihengJiang/mxnet,piiswrong/mxnet,gautamkmr/incubator-mxnet,lxn2/mxnet,dmlc/mxnet,wangyum/mxnet,solin319/incubator-mxnet,wangyum/mxnet,likelyzhao/mxnet,Mega-DatA-Lab/mxnet,ShownX/incubator-mxnet,precedenceguo/mxnet,eric-haibin-lin/mxnet,madjam/mxnet,CodingCat/mxnet,arank/mxnet,kkk669/mxnet,arikpoz/mxnet,jennyzhang0215/incubator-mxnet,hesseltuinhof/mxnet,jermainewang/mxnet,ZihengJiang/mxnet,eric-haibin-lin/mxnet,Northrend/mxnet,ShownX/incubator-mxnet,yuruofeifei/mxnet,jermainewang/mxnet,rahul003/mxnet,rahul003/mxnet,reminisce/mxnet,crazy-cat/incubator-mxnet,formath/mxnet,DickJC123/mxnet,jermainewang/mxnet,formath/mxnet,piiswrong/mxne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math/mxnet,Ldpe2G/mxnet,nicklhy/mxnet,navrasio/mxnet,vikingMei/mxnet,ShownX/incubator-mxnet,precedenceguo/mxnet,sxjscience/mxnet,rahul003/mxnet,jennyzhang0215/incubator-mxnet,ptrendx/mxnet,hpi-xnor/BMXNet,wangyum/mxnet,sergeykolychev/mxnet,tornadomeet/mxnet,mbaijal/incubator-mxnet,zhreshold/mxnet,Mega-DatA-Lab/mxnet,tlby/mxnet,ForkedReposBak/mxnet,hesseltuinhof/mxnet,ptrendx/mxnet,xcgoner/dist-mxnet,ptrendx/mxnet,tlby/mxnet,rahul003/mxnet,leezu/mxnet,indhub/mxnet,DR08/mxnet,pluskid/mxnet,solin319/incubator-mxnet,gautamkmr/incubator-mxnet,gautamkmr/incubator-mxnet,eric-haibin-lin/mxnet,mbaijal/incubator-mxnet