hack/scripts: update comments on "build-docker-release-master"
hack/scripts: update comments on "build-docker-release-master"

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

rnaveiras/etcd,bdarnell/etcd,glevand/coreos--etcd,rnaveiras/etcd,glevand/coreos--etcd,coreos/etcd,li-ang/etcd,lorneli/etcd,etcd-io/etcd,etcd-io/etcd,sebrandon1/etcd,etcd-io/etcd,gyuho/etcd,sinsharat/etcd,fanminshi/etcd,vimalk78/etcd,rnaveiras/etcd,joshix/etcd,mqliang/etcd,mqliang/etcd,lorneli/etcd,vimalk78/etcd,ajityagaty/etcd,xiang90/etcd,sinsharat/etcd,dannysauer/etcd,bdarnell/etcd,xiang90/etcd,cockroachdb/etcd,dannysauer/etcd,mqliang/etcd,mkumatag/etcd,joshix/etcd,sebrandon1/etcd,fanminshi/etcd,coreos/etcd,cockroachdb/etcd,mkumatag/etcd,ajityagaty/etcd,li-ang/etcd,ajityagaty/etcd,mkumatag/etcd,gyuho/etcd