[docs] add release notes

doc/release-notes.md

@@ -65,9 +65,28 @@ Notable changes
 P2P and network changes
 -----------------------
 
+- The mempool now tracks whether transactions submitted via the wallet or RPCs
+  have been successfully broadcast. Every 10-15 minutes, the node will try to
+  announce unbroadcast transactions until a peer requests it via a `getdata`
+  message or the transaction is removed from the mempool for other reasons.
+  The node will not track the broadcast status of transactions submitted to the
+  node using P2P relay. This version reduces the initial broadcast guarantees
+  for wallet transactions submitted via P2P to a node running the wallet. (#18038)
+
 Updated RPCs
 ------------
 
+- `getmempoolinfo` now returns an additional `unbroadcastcount` field. The
+  mempool tracks locally submitted transactions until their initial broadcast
+  is acknowledged by a peer. This field returns the count of transactions
+  waiting for acknowledgement.
+
+- Mempool RPCs such as `getmempoolentry` and `getrawmempool` with
+  `verbose=true` now return an additional `unbroadcast` field. This indicates
+  whether initial broadcast of the transaction has been acknowledged by a
+  peer. `getmempoolancestors` and `getmempooldescendants` are also updated.
+
+
 Changes to Wallet or GUI related RPCs can be found in the GUI or Wallet section below.
 
 New RPCs
@@ -87,6 +106,13 @@ New settings
 Wallet
 ------
 
+- To improve wallet privacy, the frequency of wallet rebroadcast attempts is
+  reduced from approximately once every 15 minutes to once every 12-36 hours.
+  To maintain a similar level of guarantee for initial broadcast of wallet
+  transactions, the mempool tracks these transactions as a part of the newly
+  introduced unbroadcast set. See the "P2P and network changes" section for
+  more information on the unbroadcast set. (#18038)
+
 #### Wallet RPC changes
 
 - The `upgradewallet` RPC replaces the `-upgradewallet` command line option.