coverScreen property added

Author: maxs15

README.md

@@ -36,6 +36,7 @@ Check [index.js](https://github.com/maxs15/react-native-modalbox/blob/master/Exa
 | easing | Easing.elastic(0.8) | `function` | Easing function applied to opening modal animation
 | backButtonClose | false | `bool` | (Android only) Close modal when receiving back button event
 | startOpen | false | `bool` | Allow modal to appear open without animation upon first mount
+| coverScreen | false | `bool` | Will use RN `Modal` component to cover the entire screen wherever the modal is mounted in the component hierarchy
 
 ## Events