[doc] Add hint about getmempoolentry to getrawmempool help.

Github-Pull: #10310
Rebased-From: 3a0a5bc

src/rpc/blockchain.cpp

@@ -417,6 +417,7 @@ UniValue getrawmempool(const JSONRPCRequest& request)
         throw runtime_error(
             "getrawmempool ( verbose )\n"
             "\nReturns all transaction ids in memory pool as a json array of string transaction ids.\n"
+            "\nHint: use getmempoolentry to fetch a specific transaction from the mempool.\n"
             "\nArguments:\n"
             "1. verbose (boolean, optional, default=false) True for a json object, false for array of transaction ids\n"
             "\nResult: (for verbose = false):\n"