Update README.md

Author: Pavlo Aksonov

README.md

@@ -16,6 +16,7 @@ Router for React Native based on new React Native Navigation API.
 ## Beta status
 - This version is beta, for more stable work use 2.x version from `2.x` branch,
 [README for 2.x](https://github.com/aksonov/react-native-router-flux/blob/2.x/README.md)
+- React Native 0.22-rc is supported, it could not work with earlier or later versions
 
 ## IMPORTANT! Breaking changes comparing with 2.x version:
 - `Router` is root container now and should not be nested. For nested scenes you should use `Scene` element