message: docs: use intra-doc link
diff: //! # }
  //! ```
  //!
  -//! > **A note about creating card tokens**: Stripe introduced the PaymentIntent api
  +//! > **A note about creating card tokens**: Stripe introduced the [PaymentIntent](crate::PaymentIntent) api
  //! > to replace the old token and charge API. This library only supports the former. To migrate, you can
  //! > have a look at [the official migration guide](https://stripe.com/docs/payments/payment-intents/migration).
  