add legacy link

404.html

@@ -20,7 +20,7 @@ <h1>Oops!</h1>
             <div class="column text-center">
                 <a href="{{ site.baseurl }}/" class="button large">Go Back to the Home Page</a>
                 <hr class="invisible">
-                <h6>If you really, <em>really</em> want to go back to the old website, then go <a href="{{ site.baseurl }}/">here [ someone needs to fix this link at deployment ]</a>.</h6>
+                <h6>If you really, <em>really</em> want to go back to the old website, then go <a href="https://www-legacy.openmicroscopy.org/" target="_blank">here</a>.</h6>
             </div>
         </div>     
         <hr class="whitespace">