docs: update release notes

Author: ellemouton

docs/release-notes/release-notes-0.18.0.md

@@ -289,6 +289,10 @@
   [2](https://github.com/lightningnetwork/lnd/pull/8253).
   [3](https://github.com/lightningnetwork/lnd/pull/8254).
 
+* Update the [gossip 
+  protocol](https://github.com/lightningnetwork/lnd/pull/8255) to be able to 
+  gossip new Gossip 1.75 messages. 
+
 ## Testing
 
 * Added fuzz tests for [onion