docs: add release-notes.

docs/release-notes/release-notes-0.18.3.md

@@ -40,6 +40,10 @@
   compatible](https://github.com/lightningnetwork/lnd/pull/8941) with inbound
   fees.
   
+* [Fixed](https://github.com/lightningnetwork/lnd/pull/8946) a case where 
+bumping an anchor channel closing was not possible when no HTLCs were on the
+commitment when the channel was force closed.
+
 # New Features
 ## Functional Enhancements
 ## RPC Additions