docs: update release notes for itest refactor

docs/release-notes/release-notes-0.16.0.md

@@ -185,7 +185,9 @@ The `lntest` has been
 better testing suite for writing integration tests. A new defined structure is
 implemented, please refer to
 [README](https://github.com/lightningnetwork/lnd/tree/master/lntemp) for more
-details.
+details. Along the way, several
+PRs([6776](https://github.com/lightningnetwork/lnd/pull/6776)) have been made
+to refactor the itest for code health and maintenance.
 
 # Contributors (Alphabetical Order)