invoicerpc: add clarifying comment.

lnrpc/invoicesrpc/utils.go

@@ -187,6 +187,8 @@ func CreateRPCInvoice(invoice *invoices.Invoice,
 		AmtPaidSat:      int64(satAmtPaid),
 		AmtPaidMsat:     int64(invoice.AmtPaid),
 		AmtPaid:         int64(invoice.AmtPaid),
+		// This will be set to SETTLED if at least one of the AMP Sets
+		// is settled (see below).
 		State:       state,
 		Htlcs:       rpcHtlcs,
 		Features:    CreateRPCFeatures(invoice.Terms.Features),