README: warn about repository transfer
README: warn about repository transfer

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

mkumatag/etcd,coreos/etcd,etcd-io/etcd,ajityagaty/etcd,rnaveiras/etcd,mqliang/etcd,ajityagaty/etcd,rnaveiras/etcd,gyuho/etcd,li-ang/etcd,dannysauer/etcd,joshix/etcd,ajityagaty/etcd,mkumatag/etcd,cockroachdb/etcd,gyuho/etcd,mqliang/etcd,mkumatag/etcd,xiang90/etcd,dannysauer/etcd,joshix/etcd,vimalk78/etcd,li-ang/etcd,etcd-io/etcd,sinsharat/etcd,sinsharat/etcd,mqliang/etcd,cockroachdb/etcd,vimalk78/etcd,etcd-io/etcd,xiang90/etcd,rnaveiras/etcd,coreos/etcd