Add release note for ephemeral dust

doc/release-notes-30239.md

@@ -0,0 +1,12 @@
+P2P and network changes
+-----------------------
+
+Ephemeral dust is a new concept that allows a single
+dust output in a transaction, provided the transaction
+is zero fee. In order to spend any unconfirmed outputs
+from this transaction, the spender must also spend
+this dust in addition to any other outputs.
+
+In other words, this type of transaction
+should be created in a transaction package where
+the dust is both created and spent simultaneously.