docs: startTransition in React Native (#181)

Author: kwasniew

README.md

@@ -265,6 +265,8 @@ Wrap your components like so:
 
 ## React Native
 
+### localStorage
+
 IMPORTANT: This no longer comes included in the unleash-proxy-client-js library. You will need to install the storage adapter for your preferred storage solution.
 
 Because React Native doesn't run in a web browser, it doesn't have access to the `localStorage` API. Instead, you need to tell Unleash to use your specific storage provider. The most common storage provider for React Native is [AsyncStorage](https://github.com/react-native-async-storage/async-storage).
@@ -282,6 +284,13 @@ const config = {
 };
 ```
 
+### startTransition
+
+If your version of React Native doesn't support `startTransition`, you can provide fallback implementation:
+```jsx
+  <FlagProvider startTransition={fn => fn()} ></FlagProvider>
+```
+
 # Migration guide
 
 ## Upgrade path from v1 -> v2