feat(Documentation/api): document file upload
feat(Documentation/api): document file upload

This gets asked about a lot int IRC/mailinglist/etc. Fixes this issue:
https://github.com/coreos/etcd/issues/383#issuecomment-31183603

kkaneda/etcd,arthurcolle/etcd,fgbreel/etcd,Ulexus/etcd,justintung/etcd,siddontang/etcd,nekto0n/etcd,crandles/etcd,spotify/etcd,buaazp/etcd,mgoelzer/etcd-fork2,qqsun8819/etcd,qqsun8819/etcd,Winslett/etcd,CrazyJvm/etcd,yudai/etcd,mwitkow/etcd,improbable-io/etcd,SivagnanamCiena/etcd,junxu/etcd,sebrandon1/etcd,oscarrr110/etcd,armstrongli/etcd,rchicoli/etcd,glevand/coreos--etcd,chai2010-playground/etcd,tangkun75/etcd,shafreeck/etcd,sayden/etcd,pauldallen/etcd,spotify/etcd,beni55/etcd,wantonsolutions/dinv-etcd,njucslqq/etcd,polvi/etcd,junxu/etcd,luxas/etcd,tguangch/etcd,lorneli/etcd,hzy001/etcd,glensc/etcd,es-chow/etcd,mischief/etcd,shakefu/etcd,mkumatag/etcd,joshix/etcd,dterei/etcd,plasticbox/etcd,etcd-io/etcd,dnaeon/etcd,bdarnell/etcd,Timer/etcd,chenbaihu/etcd,achanda/etcd,kkaneda/etcd,beni55/etcd,shafreeck/etcd,sebrandon1/etcd,imzhulei/etcd,chai2010/etcd,StorReduce/etcd,westhood/etcd,glevand/coreos--etcd,vimalk78/etcd,snailwalker/etcd,betawaffle/etcd,li-ang/etcd,polvi/etcd,jravetch/etcd,akauppi/etcd,sofuture/etcd,dnaeon/etcd,wfxiang08/etcd,whuwxl/etcd,robszumski/etcd,whuwxl/etcd,qiaochao911/etcd,lorneli/etcd,bluebreezecf/etcd,heyitsanthony/etcd,youxidev/etcd,freeloop1114/etcd,jchauncey/etcd,freeloop1114/etcd,giantswarm/etcd,heyitsanthony/etcd,elimisteve/etcd,msanterre/etcd,etcd-io/etcd,mkumatag/etcd,handsomesun/etcd,imzhulei/etcd,njharman/etcd,csuideal/etcd,coreos/etcd,YuleiXiao/etcd,shakefu/etcd,xychu/etcd,purpleidea/etcd,CrazyJvm/etcd,cockroachdb/etcd,wfxiang08/etcd,devfreesg/etcd,asim/etcd,xiang90/etcd,cvik/etcd,Eagle-X/etcd,tamird/etcd,xiang90/etcd,mitake/etcd,rnaveiras/etcd,ajityagaty/etcd,offscale/etcd,QuantiumTechnology/etcd,Ulexus/etcd,visheshnp/etcd,jefby/etcd,crandles/etcd,dalanlan/etcd,xebitstudios/etcd,jeremyeder/etcd,handsomesun/etcd,hongbinz/etcd,sebschrader/etcd,mkumatag/etcd,spotify/etcd,joshix/etcd,svdata/etcd,cchamplin/etcd,jefby/etcd,cockroachdb/etcd,asim/etcd,chenbaihu/etcd,mike-lerch/etcd,tempbottle/etcd,jmptrader/etcd,plasticbox/etcd,nkhare/etcd,robszumski/etcd,yyljlyy/etcd,TheHippo/etcd,mwitkow/etcd,gae123/etcd,msanterre/etcd,fanminshi/etcd,qiaochao911/etcd,QuantiumTechnology/etcd,chai2010-playground/etcd,xueshanf/etcd,Ulexus/etcd,raoofm/etcd,rnaveiras/etcd,princeqjzh/etcd,a-robinson/etcd,ecnahc515/etcd,Winslett/etcd,chai2010/etcd,ajityagaty/etcd,sofuture/etcd,tangkun75/etcd,gityf/etcd,mwitkow-io/etcd,YuleiXiao/etcd,jchauncey/etcd,gosharplite/etcd,jonboulle/etcd,hongchaodeng/etcd,iamqizhao/etcd,tguangch/etcd,endocode/etcd,wowsoso/etcd,rchicoli/etcd,honeyqa/etcd,ylong/etcd,armstrongli/etcd,sinsharat/etcd,li-ang/etcd,kingland/etcd,princeqjzh/etcd,bspline/etcd,spotify/etcd,cchamplin/etcd,siddontang/etcd,combk8s/etcd,insionng/etcd,gtank/etcd,etcd-io/etcd,yifan-gu/etcd,yifan-gu/etcd,dterei/etcd,Timer/etcd,lzbgt/etcd,insequent/etcd,hongchaodeng/etcd,gyuho/etcd,mischief/etcd,barakmich/etcd,zaphod-concur/etcd,sayden/etcd,ravigadde/etcd,cognusion/etcd,ajityagaty/etcd,combk8s/etcd,endocode/etcd,gouyang/etcd,cognusion/etcd,dannysauer/etcd,glensc/etcd,SivagnanamCiena/etcd,vimalk78/etcd,devfreesg/etcd,delkyd/etcd,Yhgenomics/etcd,sinsharat/etcd,shawnps/etcd,snailwalker/etcd,improbable-io/etcd,coreos/etcd,betawaffle/etcd,raoofm/etcd,justintung/etcd,ktateish/etcd,nkhare/etcd,giantswarm/etcd,pauldallen/etcd,ylong/etcd,offscale/etcd,glycerine/etcd,mqliang/etcd,nieanan/etcd,steveeJ/etcd,jmptrader/etcd,westhood/etcd,HideoYamauchi/etcd,Yhgenomics/etcd,linuxcer/etcd,kingland/etcd,Eagle-X/etcd,hzy001/etcd,ravigadde/etcd,hpcloud/etcd,wantonsolutions/dinv-etcd,mitake/etcd,OyTao/etcd_learning,iamqizhao/etcd,bakins/etcd,fgbreel/etcd,Ulexus/etcd,svdata/etcd,gityf/etcd,lzbgt/etcd,wowsoso/etcd,jonboulle/etcd,bspline/etcd,elimisteve/etcd,ktateish/etcd,hpcloud/etcd,nekto0n/etcd,honeyqa/etcd,mike-lerch/etcd,achanda/etcd,cvik/etcd,onlyjob/etcd,gae123/etcd,xebitstudios/etcd,mgoelzer/etcd-fork2,cvik/etcd,lumjjb/etcd,StorReduce/etcd,akauppi/etcd,purpleidea/etcd,pengzj/etcd,steveeJ/etcd,spacejam/etcd,onlyjob/etcd,nieanan/etcd,fanminshi/etcd,openedbox/etcd,tempbottle/etcd,njucslqq/etcd,spacejam/etcd,luxas/etcd,sebschrader/etcd,dalanlan/etcd,fasaxc/etcd,jravetch/etcd,linuxcer/etcd,dannysauer/etcd,zaphod-concur/etcd,xueshanf/etcd,gtank/etcd,bluebreezecf/etcd,openedbox/etcd,xdlinear/etcd,hroyrh/etcd,arthurcolle/etcd,buaazp/etcd,OyTao/etcd_learning,xdlinear/etcd,yichengq/etcd,youxidev/etcd,bdarnell/etcd,fasaxc/etcd,yudai/etcd,chipironcin/etcd,oscarrr110/etcd,a-robinson/etcd,jlamillan/etcd,axingblog/etcd,swingbach/etcd,HideoYamauchi/etcd,hongbinz/etcd,pigfoot/etcd,barakmich/etcd,olark/etcd,insionng/etcd,axingblog/etcd,cvik/etcd,yichengq/etcd,ecnahc515/etcd,mqliang/etcd,gosharplite/etcd,glycerine/etcd,gouyang/etcd,TheHippo/etcd,jeremyeder/etcd,yyljlyy/etcd,es-chow/etcd,lumjjb/etcd,hroyrh/etcd,chipironcin/etcd,csuideal/etcd,tamird/etcd,mqliang/etcd,rnaveiras/etcd,insequent/etcd,njharman/etcd,gyuho/etcd,pengzj/etcd,jlamillan/etcd,fasaxc/etcd,olark/etcd,swingbach/etcd,wantonsolutions/dinv-etcd,mwitkow-io/etcd,shawnps/etcd,bakins/etcd,delkyd/etcd,mickep76/etcd,mickep76/etcd,visheshnp/etcd,xychu/etcd