docs: update release notes

Author: yyforyongyu

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

@@ -204,7 +204,9 @@ bitcoin peers' feefilter values into account](https://github.com/lightningnetwor
   by default, and the feature is not yet advertised to the network.
 
 * Introduced [fee bumper](https://github.com/lightningnetwork/lnd/pull/8424) to
-  handle bumping the fees of sweeping transactions properly.
+  handle bumping the fees of sweeping transactions properly. A
+  [README.md](https://github.com/lightningnetwork/lnd/pull/8674) is added to
+  explain this new approach.
 
 ## RPC Additions