ACP / Style Manager / YOUR STYLE / Edit Templates / Footer
Then find this.
Code:
<vb:if condition="$vboptions['archiveenabled']"><li><a href="archive/index.php{vb:raw session.sessionurl_q}">{vb:rawphrase archive}</a></li></vb:if>
And add your link after it or before it or whatever. Thats the archive link.
So just add something like this.
Code:
<a href="http://www.YOURDOMAIN.com">YOUR TEXT</a>