Adds introduction to responsive

Related to #974

Can be invoked by:

```
<?xml version="1.0" encoding="UTF-8" ?>
<phpdocumentor>
    <introduction><![CDATA[
      <h3>Introduction</h3>
      <p>This is the 'Responsive' look and feel for phpDocumentor.</p>

      <p>This is a responsive template that is optimized to make the user's
      experience paramount.</p>

      <p>To improve performance you can add the following to your .htaccess:</p>
      <pre>
      &lt;ifModule mod_deflate.c&gt;
          &lt;filesMatch "\.(js|css|html)$"&gt;
              SetOutputFilter DEFLATE
          &lt;/filesMatch&gt;
      &lt;/ifModule&gt;
      </pre>
  ]]></introduction>
    <translator>
        <locale>de</locale>
    </translator>
</phpdocumentor>
```