message: update doc on `PrepaidCard.faceValue`
diff: @@ -438,6 +438,12 @@ This method returns a promise for an object shaped like:
  }
  ```
  +### `PrepaidCard.faceValue`
  +This call will return a promise for the most current face value of a prepaid card.
  +```js
  +let faceValue = await prepaidCard.faceValue(prepaidCardAddress);
  +```
  +
  ### `PrepaidCard.canSplit`
  This call will return a promise for a boolean indicating if the prepaid card can be split.
  ```js
  