Add note in usage output about protocol requirements for hashrate rep…

…orting

Fixes ethereum-mining#272

ethminer/MinerAux.h

@@ -546,7 +546,7 @@ class MinerCLI
 			<< "    -SC, --stratum-client <n>  Stratum client version. Defaults to 1 (async client). Use 2 to use the new synchronous client." << endl
 			<< "    -SP, --stratum-protocol <n> Choose which stratum protocol to use:" << endl
 			<< "        0: official stratum spec: ethpool, ethermine, coinotron, mph, nanopool (default)" << endl
-			<< "        1: eth-proxy compatible: dwarfpool, f2pool, nanopool" << endl
+			<< "        1: eth-proxy compatible: dwarfpool, f2pool, nanopool (required for hashrate reporting to work with nanopool)" << endl
 			<< "        2: EthereumStratum/1.0.0: nicehash" << endl
 			<< "    -RH, --report-hashrate Report current hashrate to pool (please only enable on pools supporting this)" << endl
 			<< "    -SE, --stratum-email <s> Email address used in eth-proxy (optional)" << endl