Update documentation

docs/Reference.md

 - [`onMessage`](Reference.md#onmessage)
 - [`onNavigationStateChange`](Reference.md#onnavigationstatechange)
 - [`onContentProcessDidTerminate`](Reference.md#oncontentprocessdidterminate)
+- [`onScroll`](Reference.md#onscroll)
 - [`originWhitelist`](Reference.md#originwhitelist)
 - [`renderError`](Reference.md#rendererror)
 - [`renderLoading`](Reference.md#renderloading)
 
 ---
 
+### `onScroll`[⬆](#props-index)<!-- Link generated with jump2header -->
+
+Function that is invoked when the scroll event is fired in the `WebView`.
+
+| Type     | Required | Platform                |
+| -------- | -------- | ----------------------- |
+| function | No       | iOS, macOS, Android, Windows |
+
+Example:
+
+```jsx
+<Webview
+  source={{ uri: 'https://reactnative.dev' }}
+  onScroll={syntheticEvent => {
+    const { contentOffset } = syntheticEvent.nativeEvent
+    console.table(contentOffset)
+  }}
+/>
+```
+
+Function will receive event object of `NativeSyntheticEvent<NativeScrollEvent>`
+type as an argument.
+
+---
+
 ### `originWhitelist`[⬆](#props-index)<!-- Link generated with jump2header -->
 
 List of origin strings to allow being navigated to. The strings allow wildcards and get matched against _just_ the origin (not the full URL). If the user taps to navigate to a new page but the new page is not in this whitelist, the URL will be handled by the OS. The default whitelisted origins are "http://*" and "https://*".