Update games.html

Author: mrbid

games.html

@@ -84,6 +84,7 @@ <h3>Real-time strategy</h3>
     <a href="https://serfs-game.com/">Serfs</a><br/>
     <a href="https://mindustrygame.github.io/">Mindustry</a><br/>
     <a href="https://quasilyte.itch.io/roboden">Roboden</a><br/>
+    <a href="https://www.openttd.org/">OpenTTD</a><br/>
 
     <h3>Online</h3>
     <a href="https://www.tuxemon.org">Tuxemon</a><br/>