Add release note for size 2 package rbf

Author: instagibbs

doc/release-28984.md

@@ -0,0 +1,6 @@
+P2P and network changes
+-----------------------
+
+- Limited package RBF is now enabled, where the proposed conflicting package would result in
+  a connected component, aka cluster, of size 2 in the mempool. All clusters being conflicted
+  against must be of size 2 or lower.