nit: add test doc

Co-authored-by: Matt Corallo <649246+TheBlueMatt@users.noreply.github.com>

lightning/src/ln/payment_tests.rs

@@ -1114,7 +1114,7 @@ fn do_test_dup_htlc_onchain_doesnt_fail_on_reload(persist_manager_post_event: bo
 	let funding_txo = OutPoint { txid: funding_tx.txid(), index: 0 };
 
 	// Note that we skip persisting ChannelMonitors. We should still be generating the payment sent
-	// event without ChannelMonitor persistence.
+	// event without ChannelMonitor persistence. If we reset to a previous state on reload, the block should be replayed and we'll regenerate the event.
 
 	// If we persist the ChannelManager here, we should get the PaymentSent event after
 	// deserialization.