Add a screenshot on the front page.

web/index.html

@@ -10,6 +10,7 @@
 <div class="content">
 <p>The Roguelike Gallery is a living museum of <a href="http://en.wikipedia.org/wiki/Roguelike">roguelike</a> games. A collection 
 of historical roguelikes is being restored and made available for play on this server.</p>
+<p class="cimage"><img src="screen.png" alt="Screenshot"></p>
 <p>Using the <a href="http://rlgallery.org:8080/">Web app</a>, you can try the games in your Web browser.</p>
 <p>You can also play by ssh to rlgallery.org.  The username is "rodney", and "yendor" is the password.</p>
 <h2>Available Games</h2>

web/main.css

@@ -25,6 +25,10 @@ div.nav {
 	padding: 0.3em;
 }
 
+p.cimage {
+	text-align: center;
+}
+
 ul {
 	list-style-type: none;
 }