docs: add ready to copy-paste example in README

Author: ferrannp

README.md

@@ -86,30 +86,28 @@ protected List<ReactPackage> getPackages() {
 ## Usage
 
 ```js
-import ViewPager from "@react-native-community/viewpager";
-
-class MyPager extends React.Component { 
-  render() {
-    return (
-      <ViewPager
-        style={styles.viewPager}
-        initialPage={0}>
-        <View key="1">
-          <Text>First page</Text>
-        </View>
-        <View key="2">
-          <Text>Second page</Text>
-        </View>
-      </ViewPager>
-    );
-  }
-}
+import React from 'react';
+import {StyleSheet, View, Text} from 'react-native';
+import ViewPager from '@react-native-community/viewpager';
+
+const MyPager = () => {
+  return (
+    <ViewPager style={styles.viewPager} initialPage={0}>
+      <View key="1">
+        <Text>First page</Text>
+      </View>
+      <View key="2">
+        <Text>Second page</Text>
+      </View>
+    </ViewPager>
+  );
+};
 
 const styles = StyleSheet.create({
   viewPager: {
-    flex: 1
+    flex: 1,
   },
-})
+});
 ```
 
 ## API