Make "The Basics" flow like a linear tutorial

Summary: Closes https://github.com/facebook/react-native/pull/8429

Differential Revision: D3487369

Pulled By: lacker

fbshipit-source-id: 59b32f2a2a67370192c91dc43da3d4b76a43b810

docs/HandlingTextInput.md

@@ -0,0 +1,46 @@
+---
+id: handling-text-input
+title: Handling Text Input
+layout: docs
+category: The Basics
+permalink: docs/handling-text-input.html
+next: using-a-scrollview
+---
+
+[`TextInput`](/react-native/docs/textinput.html#content) is a basic component that allows the user to enter text. It has an `onChangeText` prop that takes
+a function to be called every time the text changed.
+
+This example shows how to count the number of characters that have been typed in a box.
+
+```ReactNativeWebPlayer
+import React, { Component } from 'react';
+import { AppRegistry, Text, TextInput, View } from 'react-native';
+
+class CharacterCounter extends Component {
+  constructor(props) {
+    super(props);
+    this.state = {text: ''};
+  }
+
+  render() {
+    return (
+      <View style={{padding: 10}}>
+        <TextInput
+          style={{height: 40}}
+          placeholder="Pleeeease type on me!"
+          onChangeText={(text) => this.setState({text})}
+        />
+        <Text style={{padding: 10}}>{this.state.text.length}</Text>
+      </View>
+    );
+  }
+}
+
+AppRegistry.registerComponent('CharacterCounter', () => CharacterCounter);
+```
+
+In this example, we store `text` in the state, because it changes over time.
+
+There are a lot more advanced things you might want to do with a text input. For example, you could validate the text inside while the user types. For more detailed examples, see the [React docs on controlled components](https://facebook.github.io/react/docs/forms.html), or the [reference docs for TextInput](/react-native/docs/textinput.html).
+
+Text input is probably the simplest example of a component whose state naturally changes over time. Next, let's look at another type of component like this is one that controls layout, and [learn about the ScrollView](/react-native/docs/using-a-scrollview.html).