docs: update release note

docs/release-notes/release-notes-0.16.1.md

@@ -10,6 +10,12 @@
 * [Return `FEE_INSUFFICIENT` before checking balance for incoming low-fee
   HTLCs.](https://github.com/lightningnetwork/lnd/pull/7490).
 
+## RPC
+
+- A [debug log](https://github.com/lightningnetwork/lnd/pull/7514) has been
+  added to `lnrpc` so the node operator can know whether a certain request has
+  happened or not.
+
 # Contributors (Alphabetical Order)
 
 * Oliver Gugger