doc: use cases

docs/design/use-cases.md

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+# Use Cases
+
+## Pay someone
+The client pays a business or peer by scanning their QR code or clicking their URL.
+They are then shown the payment (send) screen that already contains the prefilled recipient and currency amount.
+The client then confirms payment with a button and optional confirmation dialog.
+
+## Request payment
+The business requests payment from a client by sharing their URL / QR code.
+The client proceeds with the `Pay someone` flow.
+
+## 
+
+## Visitor
+Visitors obtain access by receiving credentials of a predefined visitor account.
+Upon login, they participate freely in the payment process as described by `Pay someone` and `Request payment`.
+
+## Onboarding users
+An administrator performs onboarding using a batch import feature that makes use of `.csv` or a similarly simple format.