docs: update release notes for NoOp HTLCs

Author: GeorgeTsagk

docs/release-notes/release-notes-0.20.0.md

@@ -40,6 +40,13 @@
 
 # New Features
 
+- Added [NoOp HTLCs](https://github.com/lightningnetwork/lnd/pull/9871). This
+allows sending HTLCs to the remote party without shifting the balances of the
+channel. This is currently only possible to use with custom channels, and only
+when the appropriate TLV flag is set. This allows for HTLCs carrying metadata to
+reflect their state on the channel commitment without having to send or receive
+a certain amount of msats.
+
 ## Functional Enhancements
 
 * RPCs `walletrpc.EstimateFee` and `walletrpc.FundPsbt` now