Update documentation on compatibility

Author: wojtekmaj

packages/react-datetime-picker/README.md

@@ -39,7 +39,8 @@ Your project needs to use React 16.3 or later. If you use an older version of Re
 
 | React version | Newest compatible React-DateTime-Picker version |
 | ------------- | ----------------------------------------------- |
-| ≥16.3         | latest                                          |
+| ≥16.8         | latest                                          |
+| ≥16.3         | 4.x                                             |
 | ≥16.0         | 2.x                                             |
 
 [React-Calendar](https://github.com/wojtekmaj/react-calendar), on which React-DateTime-Picker relies heavily, uses modern web technologies. That's why it's so fast, lightweight and easy to style. This, however, comes at a cost of [supporting only modern browsers](https://caniuse.com/#feat=internationalization).