Record automatic currency account validation and delivery (#72)

docs/payments.md

@@ -87,7 +87,7 @@ and payout bindings remain separate from creation of the currency accounts.
 
 Deploy [Sendico #2968](https://git.sendico.io/tech/sendico/issues/2968) first:
 Ledger (including its unique index), then Product Edge, then SXCHNGE backend and
-frontend from [task #72](https://git.sendico.io/tech/sxchnge/issues/72). The public
+frontend from [PR #73](https://git.sendico.io/tech/sxchnge/pulls/73). The public
 ledger list must advertise `externalSubjectAccounts: true` before SXCHNGE sends
 any create requests. Older providers fail safely without creating accounts.
 The acknowledgement assumes Ledger and Edge are deployed in that order; it