Included are 3 files: bb-memberlist.php which goes into the my-plugins directory, mlist.php which goes into the forums root directory, and memberlist.php which goes into the template directory (whichever template you are using)
Once those three files are in place, simply put the following wherever you want the link:
<a href="<?php bb_memberlist_link(); ?>">Member List</a>
I put mine under the "Views" section
If you need rewrite rules in .htaccess, add the following line (if you don't know what that means, don't worry about it)
RewriteRule ^mlist/ /forums/mlist.php? [L,QSA]