doc: fix https omission in documentation.
doc: fix https omission in documentation.

doc: added missing (http)s to tls setup guide

This fixes a minor documentation omission, where the 1st initial-advertise-peer-url for tls setup appears to be http.

fixes documentation
wantonsolutions/dinv-etcd,hongchaodeng/etcd,ravigadde/etcd,insequent/etcd,etcd-io/etcd,cockroachdb/etcd,qqsun8819/etcd,swingbach/etcd,fanminshi/etcd,armstrongli/etcd,jonboulle/etcd,sofuture/etcd,rnaveiras/etcd,coreos/etcd,whuwxl/etcd,CrazyJvm/etcd,rnaveiras/etcd,rchicoli/etcd,plasticbox/etcd,jonboulle/etcd,ajityagaty/etcd,luxas/etcd,westhood/etcd,mkumatag/etcd,sofuture/etcd,coreos/etcd,mqliang/etcd,sebrandon1/etcd,endocode/etcd,dannysauer/etcd,li-ang/etcd,CrazyJvm/etcd,OyTao/etcd_learning,YuleiXiao/etcd,jlamillan/etcd,tguangch/etcd,zaphod-concur/etcd,linuxcer/etcd,ravigadde/etcd,qqsun8819/etcd,mkumatag/etcd,purpleidea/etcd,wantonsolutions/dinv-etcd,akauppi/etcd,bluebreezecf/etcd,OyTao/etcd_learning,nekto0n/etcd,rnaveiras/etcd,insequent/etcd,ajityagaty/etcd,a-robinson/etcd,visheshnp/etcd,dannysauer/etcd,tguangch/etcd,vimalk78/etcd,armstrongli/etcd,whuwxl/etcd,yudai/etcd,linuxcer/etcd,luxas/etcd,fanminshi/etcd,glycerine/etcd,YuleiXiao/etcd,lorneli/etcd,glycerine/etcd,gyuho/etcd,dnaeon/etcd,StorReduce/etcd,a-robinson/etcd,ajityagaty/etcd,akauppi/etcd,heyitsanthony/etcd,bdarnell/etcd,vimalk78/etcd,handsomesun/etcd,joshix/etcd,hongchaodeng/etcd,handsomesun/etcd,mqliang/etcd,lumjjb/etcd,ktateish/etcd,swingbach/etcd,zaphod-concur/etcd,StorReduce/etcd,glevand/coreos--etcd,cockroachdb/etcd,xiang90/etcd,lumjjb/etcd,sinsharat/etcd,glevand/coreos--etcd,sebrandon1/etcd,joshix/etcd,chipironcin/etcd,sinsharat/etcd,wantonsolutions/dinv-etcd,heyitsanthony/etcd,etcd-io/etcd,mickep76/etcd,ktateish/etcd,rchicoli/etcd,chipironcin/etcd,mqliang/etcd,xiang90/etcd,yudai/etcd,etcd-io/etcd,mkumatag/etcd,plasticbox/etcd,westhood/etcd,bluebreezecf/etcd,gyuho/etcd,nekto0n/etcd,dnaeon/etcd,bdarnell/etcd,lorneli/etcd,li-ang/etcd,mickep76/etcd,purpleidea/etcd,endocode/etcd,visheshnp/etcd,jlamillan/etcd