Update readme with foregroundExtrapolate prop.

Author: rostislav-simonik

README.md

@@ -84,6 +84,7 @@ The `HeaderImageScrollView` handle also the following props. None is required :
 | -------- | ---- | ------- | ----------- | ------- |
 | `renderForeground` | `function` | Empty view | Function which return the component to use at foreground. The component is render in front of the header and scroll with the ScrollView. It can return a title for example.| [example](https://github.com/bamlab/react-native-image-header-scroll-view-example/blob/master/src/Pages/TvShow.js#L112) |
 | `renderFixedForeground` | `function` | Empty view | Function which return the component to use as fixed foreground. The component is displayed with the header but not affected by the overlay.| [example](https://github.com/bamlab/react-native-image-header-scroll-view-example/blob/3b9d2d0d7f71c6bf877e2d10cc65c9ab7e1b484d/src/Pages/TvShow.js#L100) |
+| `foregroundExtrapolate` | `string` | `clamp` | Optional prop that allows override extrapolate mode for foreground. Use `null` to allow extrapolation, which is usefull for using foreground as bottom title | - |
 | `foregroundParallaxRatio` | `number` | `1` | Ration for parallax effect of foreground when scrolling. If 2, the header goes up two times faster than the scroll | [example](https://github.com/bamlab/react-native-image-header-scroll-view-example/blob/master/src/Pages/Colors.js#L23) |
 | `fadeOutForeground` | `bool` | `false` | If set, add a fade out effect on the foreground when scroll up | [example](https://github.com/bamlab/react-native-image-header-scroll-view-example/blob/master/src/Pages/Colors.js#L13) |
 | `renderTouchableFixedForeground` | `function` | Empty view | Same as `renderFixedForeground` but allow to use touchable in it. [*Can cause performances issues on Android*](https://github.com/bamlab/react-native-image-header-scroll-view/issues/6)| [example](https://github.com/bamlab/react-native-image-header-scroll-view-example/blob/master/src/Pages/PullToRefresh.js#L45) |