add v2 link to readme (#1537)

* add v2 link to readme

* Update README.md

README.md

@@ -26,6 +26,7 @@ React Native Navigation provides 100% native platform navigation on both iOS and
 * [Stack Overflow](http://stackoverflow.com/questions/tagged/react-native-navigation)
 * [Chat with us](https://discord.gg/DhkZjq2)
 * Bootstrap - If you prefer to learn more about the library and the APIs through code, head over to [the bootstrap example app](https://github.com/wix/react-native-navigation-bootstrap) or the more feature rich [JuneDomingo/movieapp](https://github.com/JuneDomingo/movieapp)
+* [v2 - Under Development](https://github.com/wix/react-native-navigation/tree/v2#react-native-navigation-v2-wip)
 
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