[Doc] Clarify the meaning of fee delta not being a fee rate in prioritisetransaction RPC

Author: janbraiins

src/rpc/mining.cpp

@@ -240,6 +240,7 @@ UniValue prioritisetransaction(const JSONRPCRequest& request)
             "2. dummy          (numeric, optional) API-Compatibility for previous API. Must be zero or null.\n"
             "                  DEPRECATED. For forward compatibility use named arguments and omit this parameter.\n"
             "3. fee_delta      (numeric, required) The fee value (in satoshis) to add (or subtract, if negative).\n"
+            "                  Note, that this value is not a fee rate. It is a value to modify absolute fee of the TX.\n"
             "                  The fee is not actually paid, only the algorithm for selecting transactions into a block\n"
             "                  considers the transaction as it would have paid a higher (or lower) fee.\n"
             "\nResult:\n"