docs: add client flags to examples in clustering.md
docs: add client flags to examples in clustering.md

to make it a complete functional example

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