etcdctl: document "ETCD_WATCH_*"
etcdctl: document "ETCD_WATCH_*"

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

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