Update README.md

Author: iKrushYou

README.md

@@ -56,7 +56,10 @@ The application under ./SwipeListExample will produce the above example. To run
 ```javascript
 import { SwipeListView } from 'react-native-swipe-list-view';
 
-//... note: your data array objects MUST contain a key property or you must pass a keyExtractor to the SwipeListView to ensure proper functionality
+//... note: your data array objects MUST contain a key property 
+//          or you must pass a keyExtractor to the SwipeListView to ensure proper functionality
+//          see: https://reactnative.dev/docs/flatlist#keyextractor
+
   this.state.listViewData = Array(20)
     .fill("")
     .map((_, i) => ({ key: `${i}`, text: `item #${i}` }));