Added WP8 to readme.
Added WP8 to readme.

swiese/facebook-csharp-sdk,simpleverso/facebook-csharp-sdk,simpleverso/facebook-csharp-sdk,swiese/facebook-csharp-sdk,ladyquartermaine/facebook-csharp-sdk,facebook-csharp-sdk/facebook-csharp-sdk,facebook-csharp-sdk/facebook-csharp-sdk,ladyquartermaine/facebook-csharp-sdk