f expand a bit more on psbt

Author: TheBlueMatt

CHANGELOG.md

@@ -5,7 +5,8 @@
  * The `bitcoin` dependency has been updated to version 0.30 (#2740).
  * `lightning-invoice::payment::*` have been replaced with parameter generation
    via `payment_parameters_from[_zero_amount]_invoice` (#2727).
- * `{CoinSelection,Wallet}Source::sign_tx` are now `sign_psbt` (#2775).
+ * `{CoinSelection,Wallet}Source::sign_tx` are now `sign_psbt`, providing more
+   information, incl spent outputs, about the transaction being signed (#2775).
  * Logger `Record`s now include `channel_id` and `peer_id` fields. These are
    opportunistically filled in when a log record is specific to a given channel
    and/or peer, and may occasionally be spuriously empty (#2314).