Prettify <pre> on homepage.

docs/_layouts/home.html

@@ -19,4 +19,11 @@
 
         {% include ga.html %}
     </body>
+        <script>
+           (function () {
+              'use strict';
+
+              prettyPrint();
+            })();
+        </script>
 </html>

docs/index.html

@@ -64,7 +64,7 @@ slug: home
         Include the following lines of code in the <code>&lt;head&gt;</code>
         section of your HTML.
 
-<pre class="code">
+<pre class="code prettyprint">
 &lt;link href="//cdnjs.cloudflare.com/ajax/libs/select2/4.0.0-rc.2/css/select2.min.css" rel="stylesheet" /&gt;
 &lt;script src="//cdnjs.cloudflare.com/ajax/libs/select2/4.0.0-rc.2/js/select2.min.js"&gt;&lt;/script&gt;
 </pre>
@@ -79,7 +79,7 @@ slug: home
         Initialize Select2 on the <code>&lt;select&gt;</code> element that you
         want to make awesome.
 
-<pre class="code">
+<pre class="code prettyprint">
 &lt;script type="text/javascript"&gt;
   $('select').select2();
 &lt;/script&gt;
@@ -111,7 +111,7 @@ slug: home
         Include the following lines of code in the <code>&lt;head&gt;</code>
         section of your HTML.
 
-<pre class="code">
+<pre class="code prettyprint">
 &lt;link href="path/to/select2.min.css" rel="stylesheet" /&gt;
 &lt;script src="path/to/select2.min.js"&gt;&lt;/script&gt;
 </pre>