docs: update release notes

Author: yyforyongyu

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

@@ -70,6 +70,10 @@ circuit. The indices are only available for forwarding events saved after v0.20.
   finish under this timeout value. Consider using a larger timeout value if you
   have a slow network.
 
+* The default value for `gossip.msg-rate-bytes` has been
+  [increased](https://github.com/lightningnetwork/lnd/pull/10096) from 100KB to
+  1MB, and `gossip.msg-burst-bytes` has been increased from 200KB to 2MB.
+
 
 ## lncli Additions