Added a couple of screenshots on the web page

doc/gmsh.html

@@ -252,6 +252,13 @@ e-mails to send questions or bug reports.
 
 <h2>Gallery</h2>
 
+Everybody loves screenshots... So here are some:
+<A href="/gmsh/gallery/screenshot1.gif">screenshot 1</a>,
+<A href="/gmsh/gallery/screenshot2.gif">screenshot 2</a>,
+<A href="/gmsh/gallery/screenshot3.gif">screenshot 3</a>,
+<A href="/gmsh/gallery/screenshot4.gif">screenshot 4</a>.
+<p>
+
 Some pictures made with Gmsh:
 <ul>
 <li>Part of a shoulder bone: