add link to preprint

doc/gmsh.html

@@ -90,9 +90,15 @@ Browse all versions: <a href="/gmsh/bin/">binaries</a>
 and <a href="/gmsh/src/">sources</a>
 </ul>
 
-If you use Gmsh, we would appreciate if you could mention it in your
-work (books, articles, reports, etc.). Cite the web site for now; a
-paper is in preparation, but is not yet ready.
+If you use Gmsh, we would appreciate if you could cite the following
+reference in your work (books, articles, reports, etc.):
+``<a href="gmsh_paper_preprint.pdf">C. Geuzaine and
+J.-F. Remacle. <em>Gmsh: a three-dimensional finite element mesh
+generator with built-in pre- and post-processing
+facilities</em>. International Journal for Numerical Methods in
+Engineering, Accepted for publication, 2009</a>''. (We will update the
+reference with volume and page information as soon as the article is
+actually published.)
 
 <h2><a name="Authors"></a>Authors and credits</h2>