Reference to the "official" bindings in Readme

[bgever]

Hi, thanks for your efforts to build bindings to the TestFlight SDK. It may be good for new visitors to also be aware of the "official" bindings, see: https://github.com/mono/monotouch-bindings/tree/master/TestFlight

Therefore, I would suggest to put a reference in the Readme document.

[rolivares]

Yes, maybe official, but not updated :(