f note past ser

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -6941,6 +6941,7 @@ impl Writeable for HTLCSource {
 					(0, session_priv, required),
 					(1, payment_id_opt, option),
 					(2, first_hop_htlc_msat, required),
+					// 3 was previously used to write a PaymentSecret for the payment.
 					(4, *path, vec_type),
 					(5, None::<PaymentParameters>, option), // payment_params in LDK versions prior to 0.0.115
 				 });