update to ble gateway readme
update to ble gateway readme

ihassin/nRF51-ble-bcast-mesh,mrquincle/nRF51-ble-bcast-mesh,mrquincle/nRF51-ble-bcast-mesh,mrquincle/nRF51-ble-bcast-mesh,mrquincle/nRF51-ble-bcast-mesh,ihassin/nRF51-ble-bcast-mesh