[doc] add release note for TRUC

Author: glozow

doc/release-notes-29496.md

@@ -0,0 +1,11 @@
+Mempool Policy Changes
+----------------------
+
+- Transactions with version number set to 3 are now treated as standard on all networks (#29496),
+  subject to Opt-in Topologically Restricted Until Confirmation (TRUC) Transactions policy as
+  described in [BIP 431](https://github.com/bitcoin/bips/blob/master/bip-0431.mediawiki).  The
+  policy includes limits on spending unconfirmed outputs (#28948), eviction of a previous descendant
+  if a more incentive-compatible one is submitted (#29306), and a maximum transaction size of 10,000vB
+  (#29873). These restrictions simplify the assessment of incentive compatibility of accepting or
+  replacing TRUC transactions, thus ensuring any replacements are more profitable for the node and
+  making fee-bumping more reliable.