Merge #16467: rpc: sendrawtransaction help privacy note

07e01d6 rpc: sendrawtransaction unconditionality/privacy note (Jon Atack)

Pull request description:

  In sendrawtransaction RPCHelpMan, mention unconditionality and privacy as per http://www.erisian.com.au/bitcoin-core-dev/log-2019-07-25.html#l-522

  before

  ```
  $ bitcoin-cli help sendrawtransaction
  sendrawtransaction "hexstring" ( maxfeerate )

  Submits raw transaction (serialized, hex-encoded) to local node and network.

  Also see createrawtransaction and signrawtransactionwithkey calls.

  (...)
  ```

  after

  ```
  $ bitcoin-cli help sendrawtransaction
  sendrawtransaction "hexstring" ( maxfeerate )

  Submit a raw transaction (serialized, hex-encoded) to local node and network.

  Note that the transaction will be sent unconditionally to all peers, so using this
  for manual rebroadcast may degrade privacy by leaking the transaction's origin, as
  nodes will normally not rebroadcast non-wallet transactions already in their mempool.

  Also see createrawtransaction and signrawtransactionwithkey calls.

  (...)
  ```

ACKs for top commit:
  promag:
    ACK 07e01d6.
  laanwj:
    ACK 07e01d6

Tree-SHA512: 427b3ca29384eef271eb496b7b14e883220863543a536ddeb31940aaffd52ea0b607d929d50f2b7958514105ef7823fa05c1ee381d4a432808753c06bd97af58

Author: laanwj

src/rpc/rawtransaction.cpp

@@ -760,7 +760,10 @@ static UniValue signrawtransactionwithkey(const JSONRPCRequest& request)
 static UniValue sendrawtransaction(const JSONRPCRequest& request)
 {
     RPCHelpMan{"sendrawtransaction",
-                "\nSubmits raw transaction (serialized, hex-encoded) to local node and network.\n"
+                "\nSubmit a raw transaction (serialized, hex-encoded) to local node and network.\n"
+                "\nNote that the transaction will be sent unconditionally to all peers, so using this\n"
+                "for manual rebroadcast may degrade privacy by leaking the transaction's origin, as\n"
+                "nodes will normally not rebroadcast non-wallet transactions already in their mempool.\n"
                 "\nAlso see createrawtransaction and signrawtransactionwithkey calls.\n",
                 {
                     {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of the raw transaction"},