doc: mention P2SH IsStandard relaxation in release notes

doc/release-notes.md

@@ -195,6 +195,17 @@ correctly spends the passed scriptPubKey under additional constraints indicated
 The functionality is planned to be extended to e.g. UTXO management in upcoming releases, but the interface
 for existing methods should remain stable.
 
+Standard script rules relaxed for P2SH addresses
+================================================
+
+The IsStandard() rules have been almost completely removed for P2SH
+redemption scripts, allowing applications to make use of any valid
+script type, such as "n-of-m OR y", hash-locked oracle addresses, etc.
+While the Bitcoin protocol has always supported these types of script,
+actually using them on mainnet has been previously inconvenient as
+standard Bitcoin Core nodes wouldn't relay them to miners, nor would
+most miners include them in blocks they mined.
+
 0.10.0 Release notes
 =======================