Update example snippet in old 'React.addons' doc page (#9363)

* Update example snippet in old 'React.addons' doc page

This makes the example more consistent.

* Add back the pointers in docs that were mistakenly removed

In https://github.com/facebook/react/pull/9359 we accidentally removed
pointers in some doc pages. Putting them back now.

* Link to npm package instead of github page

This seems like a more stable place to link to in the 'context'
document.
Based on @bvaughn's feedback in https://github.com/facebook/react/pull/9359

docs/docs/addons.md

@@ -34,8 +34,8 @@ The add-ons below are considered legacy and their use is discouraged.
 You can install the add-ons individually from npm (e.g. `npm install react-addons-create-fragment`) and import them:
 
 ```javascript
-import Perf from 'react-addons-perf'; // ES6
-var Perf = require('react-addons-perf'); // ES5 with npm
+import createFragment from 'react-addons-create-fragment'; // ES6
+var createFragment = require('react-addons-create-fragment'); // ES5 with npm
 ```
 
 When using a CDN, you can use `react-with-addons.js` instead of `react.js`:

docs/docs/components-and-props.md

@@ -12,6 +12,8 @@ redirect_from:
   - "docs/transferring-props-zh-CN.html"
   - "tips/props-in-getInitialState-as-anti-pattern.html"
   - "tips/communicate-between-components.html"
+prev: rendering-elements.html
+next: state-and-lifecycle.html
 ---
 
 Components let you split the UI into independent, reusable pieces, and think about each piece in isolation.

docs/docs/composition-vs-inheritance.md

@@ -3,6 +3,8 @@ id: composition-vs-inheritance
 title: Composition vs Inheritance
 permalink: docs/composition-vs-inheritance.html
 redirect_from: "docs/multiple-components.html"
+prev: lifting-state-up.html
+next: thinking-in-react.html
 ---
 
 React has a powerful composition model, and we recommend using composition instead of inheritance to reuse code between components.

docs/docs/conditional-rendering.md

@@ -2,6 +2,8 @@
 id: conditional-rendering
 title: Conditional Rendering
 permalink: docs/conditional-rendering.html
+prev: handling-events.html
+next: lists-and-keys.html
 redirect_from: "tips/false-in-jsx.html"
 ---
 

docs/docs/context.md

@@ -5,7 +5,7 @@ permalink: docs/context.html
 ---
 
 >Note:
-> As of React v15.5 the `React.PropTypes` helper is deprecated, and we recommend using the [`prop-types` library](https://github.com/aackerman/PropTypes) to define `contextTypes`.
+> As of React v15.5 the `React.PropTypes` helper is deprecated, and we recommend using the [`prop-types` library](https://www.npmjs.com/package/prop-types) to define `contextTypes`.
 
 With React, it's easy to track the flow of data through your React components. When you look at a component, you can see which props are being passed, which makes your apps easy to reason about.