Merge bitcoin/bitcoin#33037: doc: Add release notes for 32521 (MAX_TX_LEGACY_SIGOPS)

faa2f3b doc: Add release notes for 32521 (MAX_TX_LEGACY_SIGOPS) (MarcoFalke)

Pull request description:

  ref bitcoin/bitcoin#32521

ACKs for top commit:
  Sjors:
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Tree-SHA512: 58694545eca38cd4391d2ce6ddb9f4785c19af3df639da9d17fa1ade5d56369723e0e7fece71b50e2186a65aa55919c8f64ae12833d676e07b448e0cfc53ce3c

Author: fanquake

doc/release-notes-32521.md

@@ -0,0 +1,9 @@
+### Policy
+
+The maximum number of potentially executed legacy signature operations in a
+single standard transaction is now limited to 2500. Signature operations in all
+previous output scripts, in all input scripts, as well as all P2SH redeem
+scripts (if there are any) are counted toward the limit. The new limit is
+assumed to not affect any known typically formed standard transactions. The
+change was done to prepare for a possible BIP54 deployment in the future.
+(#32521)