Documentation.

h2/src/docsrc/html/roadmap.html

@@ -530,6 +530,7 @@ See also <a href="build.html#providing_patches">Providing Patches</a>.
 </li><li>Listener or authentication module for new connections, or a way to restrict the number of different connections to a tcp server,
     or to prevent to login with the same username and password from different IPs.
     Possibly using the DatabaseEventListener API, or a new API.
+</li><li>Support ALTER TABLE ADD COLUMN IF NOT EXISTS.    
 </li></ul>
 
 <h2>Not Planned</h2>