update documentation

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

@@ -37,6 +37,9 @@
   might panic due to empty witness data found in a transaction. More details
   can be found [here](https://github.com/bitcoin/bitcoin/issues/28730).
 
+* [Fixed a case](https://github.com/lightningnetwork/lnd/pull/7503) where it's
+  possible a failed payment might be stuck in pending.
+
 # New Features
 ## Functional Enhancements
 
@@ -58,6 +61,13 @@
   [http-header-timeout](https://github.com/lightningnetwork/lnd/pull/7715), is added so users can specify the amount of time the http server will wait for a request to complete before closing the connection. The default value is 5 seconds.
 
 ## RPC Additions
+
+* [Deprecated](https://github.com/lightningnetwork/lnd/pull/7175)
+  `StatusUnknown` from the payment's rpc response in its status and added a new
+  status, `StatusInitiated`, to explicitly report its current state. Before
+  running this new version, please make sure to upgrade your client application
+  to include this new status so it can understand the RPC response properly.
+
 ## lncli Additions
 
 # Improvements
@@ -81,6 +91,12 @@
   hash](https://github.com/lightningnetwork/lnd/pull/8106) to the
   signer.SignMessage/signer.VerifyMessage RPCs.
 
+* `sendtoroute` will return an error when it's called using the flag
+  `--skip_temp_err` on a payment that's not a MPP. This is needed as a temp
+  error is defined as a routing error found in one of a MPP's HTLC attempts.
+  If, however, there's only one HTLC attempt, when it's failed, this payment is
+  considered failed, thus there's no such thing as temp error for a non-MPP.
+
 ## lncli Updates
 ## Code Health
 
@@ -90,6 +106,11 @@
   `lnrpc.GetInfoResponse` message along with the `chain` field in the
   `lnrpc.Chain` message have also been deprecated for the same reason.
 
+* The payment lifecycle code has been refactored to improve its maintainablity.
+  In particular, the complexity involved in the lifecycle loop has been
+  decoupled into logical steps, with each step having its own responsibility,
+  making it easier to reason about the payment flow.
+
 ## Breaking Changes
 ## Performance Improvements