paymentsdb: add more comments

diff --git a/lnrpc/routerrpc/router_backend.go b/lnrpc/routerrpc/router_backend.go
index d8c8a17..3085f58 100644
--- a/lnrpc/routerrpc/router_backend.go
+++ b/lnrpc/routerrpc/router_backend.go
@@ -1767,6 +1767,10 @@ func (r *RouterBackend) MarshallPayment(payment *paymentsdb.MPPayment) (
 		// If any of the htlcs have settled, extract a valid
 		// preimage.
 		if htlc.Settle != nil {
+			// For AMP payments all hashes will be different so we
+			// will only show the last htlc preimage, this is a
+			// current limitation for AMP payments because for
+			// MPP payments all hashes are the same.
 			preimage = htlc.Settle.Preimage
 			fee += htlc.Route.TotalFees()
 		}
diff --git a/payments/db/sql_converters.go b/payments/db/sql_converters.go
index fd0cad2..66f3b1d 100644
--- a/payments/db/sql_converters.go
+++ b/payments/db/sql_converters.go
@@ -27,8 +27,10 @@ func dbPaymentToCreationInfo(paymentIdentifier []byte, amountMsat int64,
 	copy(identifier[:], paymentIdentifier)
 
 	return &PaymentCreationInfo{
-		PaymentIdentifier:     identifier,
-		Value:                 lnwire.MilliSatoshi(amountMsat),
+		PaymentIdentifier: identifier,
+		Value:             lnwire.MilliSatoshi(amountMsat),
+		// The creation time is stored in the database as UTC but here
+		// we convert it to local time.
 		CreationTime:          createdAt.Local(),
 		PaymentRequest:        intentPayload,
 		FirstHopCustomRecords: firstHopCustomRecords,
@@ -205,7 +207,8 @@ func dbDataToRoute(hops []sqlc.FetchHopsForAttemptsRow,
 			)
 		}
 
-		// Add blinding point if present (only for introduction node).
+		// Add blinding point if present (only for introduction node
+		// in blinded route).
 		if len(hop.BlindingPoint) > 0 {
 			pubKey, err := btcec.ParsePubKey(hop.BlindingPoint)
 			if err != nil {