Update Networking.md

Summary:
Added an example of the Fetch usage inside a component.

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Closes https://github.com/facebook/react-native/pull/12348

Differential Revision: D4962419

Pulled By: hramos

fbshipit-source-id: 37b3517811f5391126d9e3ec026d2902705729a7

docs/Networking.md

@@ -75,6 +75,56 @@ You can also use the proposed ES2017 `async`/`await` syntax in a React Native ap
 
 Don't forget to catch any errors that may be thrown by `fetch`, otherwise they will be dropped silently.
 
+```SnackPlayer?name=Fetch%20Example
+import React, { Component } from 'react';
+import { ActivityIndicator, ListView, Text, View } from 'react-native';
+
+export default class Movies extends Component {
+  constructor(props) {
+    super(props);
+    this.state = {
+      isLoading: true
+    }
+  }
+
+  componentDidMount() {
+    return fetch('https://facebook.github.io/react-native/movies.json')
+      .then((response) => response.json())
+      .then((responseJson) => {
+        let ds = new ListView.DataSource({rowHasChanged: (r1, r2) => r1 !== r2});
+        this.setState({
+          isLoading: false,
+          dataSource: ds.cloneWithRows(responseJson.movies),
+        }, function() {
+          // do something with new state
+        });
+      })
+      .catch((error) => {
+        console.error(error);
+      });
+  }
+
+  render() {
+    if (this.state.isLoading) {
+      return (
+        <View style={{flex: 1, paddingTop: 20}}>
+          <ActivityIndicator />
+        </View>
+      );
+    }
+
+    return (
+      <View style={{flex: 1, paddingTop: 20}}>
+        <ListView
+          dataSource={this.state.dataSource}
+          renderRow={(rowData) => <Text>{rowData.title}, {rowData.releaseYear}</Text>}
+        />
+      </View>
+    );
+  }
+}
+```
+
 > By default, iOS will block any request that's not encrypted using SSL. If you need to fetch from a cleartext URL (one that begins with `http`) you will first need to add an App Transport Security exception. If you know ahead of time what domains you will need access to, it is more secure to add exceptions just for those domains; if the domains are not known until runtime you can [disable ATS completely](docs/integration-with-existing-apps.html#app-transport-security). Note however that from January 2017, [Apple's App Store review will require reasonable justification for disabling ATS](https://forums.developer.apple.com/thread/48979). See [Apple's documentation](https://developer.apple.com/library/ios/documentation/General/Reference/InfoPlistKeyReference/Articles/CocoaKeys.html#//apple_ref/doc/uid/TP40009251-SW33) for more information.
 
 ### Using Other Networking Libraries