Add renderContentBackground prop

Author: i6mi6

README.md

@@ -108,6 +108,7 @@ The `ParallaxScrollView` component adds a few additional properties, as describe
 | `onChangeHeaderVisibility` | `func` | No | A callback function that is invoked when the parallax header is hidden or shown (as the user is scrolling). Function is called with a `boolean` value to indicate whether header is visible or not. |
 | **`parallaxHeaderHeight`** | `number` | **Yes** |This is the height of parallax header. |
 | `renderBackground` | `func` | No | This renders the background of the parallax header. Can be used to display cover images for example. (Defaults to an opaque background using `backgroundColor`) |
+| `renderContentBackground` | `func` | No | This renders the background of the content. Can be used to display cover images for example. (Defaults to a non-visible `View`) |
 | `renderFixedHeader` | `func` | No | This renders an optional fixed header that will always be visible and fixed to the top of the view (and sticky header). You should set its height and width appropriately. |
 | `renderForeground` |  `func` | No |This renders the foreground header that moves at same speed as scroll content. |
 | `renderScrollComponent` | `func` | No | A function with input `props` and outputs an `Animated.ScrollView`-like component in which the content is rendered. This is useful if you want to provide your own scrollable component, remember however to make it an Animated component. (See: [https://github.com/exponentjs/react-native-scrollable-mixin](https://github.com/exponentjs/react-native-scrollable-mixin)) (By default, returns a `Animated.ScrollView` with the given props) |