Merge #15315: [0.17] [Doc] Backport release note about PSBT doc

807add9f5d [0.17] [Doc] Backport release note about PSBT doc (David A. Harding)

Pull request description:

  #15314 removes a release note from master for a doc that is backported to 0.17.  This adds the note to the 0.17 branch.  The only difference in the text is that the `master` in the URL has been changed to `0.17`.

Tree-SHA512: b81af561ad6cf608e3b957d7c50fe6d9b0818cfbd16313599d6dadb4b60e9e3345fef949c4e2ed16cdecfd62201e3e099907f1510e4d16a9f33625163c84c5a2

doc/release-notes.md

@@ -2,7 +2,7 @@ Bitcoin Core version 0.17.x is now available from:
 
   <https://bitcoincore.org/bin/bitcoin-core-0.17.x/>
 
-This is a new major version release, including new features, various bugfixes
+This is a new minor version release, including new features, various bugfixes
 and performance improvements, as well as updated translations.
 
 Please report bugs using the issue tracker at GitHub:
@@ -60,7 +60,16 @@ support versions of macOS older than 10.10.
 Notable changes
 ===============
 
-(todo)
+Documentation
+-------------
+
+- A new document introduces Bitcoin Core's BIP174
+  [Partially-Signed Bitcoin Transactions (PSBT)](https://github.com/bitcoin/bitcoin/blob/0.17/doc/psbt.md)
+  interface, which is used to allow multiple programs to collaboratively
+  work to create, sign, and broadcast new transactions.  This is useful
+  for offline (cold storage) wallets, multisig wallets, coinjoin
+  implementations, and many other cases where two or more programs need
+  to interact to generate a complete transaction.
 
 0.17.x change log
 =================