Document new upload_date template parameter

documentation.html

@@ -79,6 +79,7 @@
 <li><em>id</em>: The sequence will be replaced by the video identifier.</li>
 <li><em>url</em>: The sequence will be replaced by the video URL.</li>
 <li><em>uploader</em>: The sequence will be replaced by the nickname of the person who uploaded the video.</li>
+<li><em>upload_date</em>: The sequence will be replaced by the upload date in YYYYMMDD format.</li>
 <li><em>title</em>: The sequence will be replaced by the literal video title.</li>
 <li><em>stitle</em>: The sequence will be replaced by a simplified video title, restricted to alphanumeric characters and dashes.</li>
 <li><em>ext</em>: The sequence will be replaced by the appropriate extension (like <em>flv</em> or <em>mp4</em>).</li>