chore: Add passkit_ui link to readme

Author: ueman

README.md

@@ -7,4 +7,4 @@ This repo contains various packages to deal with PkPass files.
 | `app`           | App which makes use of the various libraries. Android only.            |                                        |
 | `apple_passkit` | Package to interface with the native functionality on iOS              | https://pub.dev/packages/apple_passkit |
 | `passkit`       | Pure Dart package to read PkPass files. Can be used on server side too | https://pub.dev/packages/passkit       |
-| `passkit_ui`    | Pure Flutter package to show PkPass files. Makes use of `passkit`      |                                        |
+| `passkit_ui`    | Pure Flutter package to show PkPass files. Makes use of `passkit`      | https://pub.dev/packages/passkit_ui    |