Minor grammatical correction

Author: Andreas Savvides

docs/welcome/index.html

@@ -412,7 +412,7 @@ <h3>Automatic page load progress bar</h3>
         <div class="section">
             <div class="page">
                 <h2>What is Pace?</h2>
-                <p style="text-align: left">Include pace.js and the theme css of your choice, and you get a beautiful progress indicator for your page load and ajax navigation.</p>
+                <p style="text-align: left">Include pace.js and a CSS theme of your choice, and you get a beautiful progress indicator for your page load and ajax navigation.</p>
                 <p style="text-align: left">No need to hook into any of your code, progress is detected automatically.</p>
                 <br/>
                 <h2>Download</h2>