Documentation/op-guide: improve compaction guide
Documentation/op-guide: improve compaction guide

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

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