docs: update release notes

docs/release-notes/release-notes-0.18.4.md

@@ -71,6 +71,10 @@ types](https://github.com/lightningnetwork/lnd/pull/8960).
 
 ## lncli Additions
 
+* [`updatechanpolicy`](https://github.com/lightningnetwork/lnd/pull/8805) will
+  now update the channel policy if the edge was not found in the graph
+  database if the `create_missing_edge` flag is set.
+
 # Improvements
 ## Functional Updates
 ## RPC Updates