update IO doc
update IO doc

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