docs: update the release-notes-0.18.0.md

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

@@ -265,6 +265,11 @@ bitcoin peers' feefilter values into account](https://github.com/lightningnetwor
   types](https://github.com/lightningnetwork/lnd/pull/8554) defined in
   `btcd/rpcclient`.
 
+* [checkOutboundPeers](https://github.com/lightningnetwork/lnd/pull/8576) is
+  added to `chainHealthCheck` to make sure chain backend `bitcoind` and `btcd`
+  maintain a healthy connection to the network by checking the number of
+  outbound peers if they are below 6.
+
 ### Logging
 * [Add the htlc amount](https://github.com/lightningnetwork/lnd/pull/8156) to
   contract court logs in case of timed-out HTLCs in order to easily spot dust