docs: update release notes for payment status

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

@@ -27,6 +27,11 @@
 # Improvements
 ## Functional Updates
 ## RPC Updates
+
+* [Deprecated](https://github.com/lightningnetwork/lnd/pull/7175)
+  `StatusUnknown` from the payment's rpc response in its status and replaced it
+  with `StatusInitiated` to explicitly report its current state.
+
 ## lncli Updates
 ## Code Health
 ## Breaking Changes
@@ -39,4 +44,6 @@
 ## Code Health
 ## Tooling and Documentation
 
-# Contributors (Alphabetical Order)
+# Contributors (Alphabetical Order)
+
+* Yong Yu