updated listsinceblock rpc docs

fixes #8758

src/wallet/rpcwallet.cpp

@@ -1650,6 +1650,7 @@ UniValue listsinceblock(const JSONRPCRequest& request)
             "    \"vout\" : n,               (numeric) the vout value\n"
             "    \"fee\": x.xxx,             (numeric) The amount of the fee in " + CURRENCY_UNIT + ". This is negative and only available for the 'send' category of transactions.\n"
             "    \"confirmations\": n,       (numeric) The number of confirmations for the transaction. Available for 'send' and 'receive' category of transactions.\n"
+            "                                          When it's < 0, it means the transaction conflicted that many blocks ago.\n"
             "    \"blockhash\": \"hashvalue\",     (string) The block hash containing the transaction. Available for 'send' and 'receive' category of transactions.\n"
             "    \"blockindex\": n,          (numeric) The index of the transaction in the block that includes it. Available for 'send' and 'receive' category of transactions.\n"
             "    \"blocktime\": xxx,         (numeric) The block time in seconds since epoch (1 Jan 1970 GMT).\n"