docs: update release notes for fee bumper

Author: yyforyongyu

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

@@ -175,6 +175,9 @@ bitcoin peers' feefilter values into account](https://github.com/lightningnetwor
 * [Preparatory work](https://github.com/lightningnetwork/lnd/pull/8159) for 
   forwarding of blinded routes was added.
 
+* Introduced [fee bumper](https://github.com/lightningnetwork/lnd/pull/8424) to
+  handle bumping the fees of sweeping transactions properly.
+
 ## RPC Additions
 
 * [Deprecated](https://github.com/lightningnetwork/lnd/pull/7175)