Update doc since PR was accepted (#3020)

The following  https://github.com/wix/react-native-navigation/pull/3006 implemented this functionality

docs/README.md

 
 |       other        | iOS  | Android | Contributor(s) |
 |--------------------|:----:|:-----:|-----|
-| screenBackgroundColor        |   ✅     |     [Contribute](/docs/WorkingLocally.md)       |  Wix |
+| screenBackgroundColor        |   ✅     | ✅ | |
 | orientation       |    ✅     |✅| Wix |
 | disabledBackGesture        |    ✅     |    / iOS specific     | |
 | screenBackgroundImageName        |   ✅      |    [Contribute](/docs/WorkingLocally.md)        | |