Docs: Basic Components Update

Summary:
This is an improvement to basic components docs.

* I updated the basic components example code to better render components on iOS (added paddingTop).
* I also modified the code to allow reader to easily copy, paste, and then run the code in their project if they followed the 'Getting Started' quick start guide.
* I also added additional copy to clarify suggested usage/guidelines.
Closes https://github.com/facebook/react-native/pull/8292

Differential Revision: D3469943

Pulled By: JoelMarcey

fbshipit-source-id: 21ff6ee13b59741c43d80aab68a38aace0fbfca6

docs/Basics-Component-TextInput.md

@@ -9,20 +9,29 @@ next: basics-component-scrollview
 
 Direct text-based user input is a foundation for many apps. Writing a post or comment on a page is a canonical example of this. [`TextInput`](/react-native/docs/textinput.html#content) is a basic component that allows the user to enter text.
 
-This example creates a simple `TextInput` box with the `string` `Hello` as the placeholder when the `TextInput` is empty.
+This example creates a simple `TextInput` box with the `string` `Type something here` as the placeholder when the `TextInput` is empty.
 
 ```JavaScript
 import React from 'react';
-import { AppRegistry, TextInput, View } from 'react-native';
+import { AppRegistry, Text, TextInput, View } from 'react-native';
 
-const App = () => {
+const AwesomeProject = () => {
   return (
-      <View>
-        <TextInput placeholder="Hello" />
-      </View>
+    <View style={{paddingTop: 22}}>
+      <TextInput
+        style={{
+          height: 40,
+          margin: 5,
+          paddingLeft: 10,
+          borderColor: 'black',
+          borderWidth: 1
+        }}
+        placeholder="Type something here"
+      />
+    </View>
   );
 }
 
 // App registration and rendering
-AppRegistry.registerComponent('MyApp', () => App);
+AppRegistry.registerComponent('AwesomeProject', () => AwesomeProject);
 ```