Add an entry in the navigation bar

index.html

@@ -23,6 +23,8 @@
             <a href="index.html" class="active">Hauptseite</a>
             <a href="https://cfp.cttue.de/tdf5/schedule" class="nav-button" target="_blank"
               rel="noopener noreferrer">Programm <span class="fas">&#xf35d;</span></a>
+            <a href="https://pretix.cttue.de/cttue/tdf5-hackertours/" class="nav-button" target="_blank"
+              rel="noopener noreferrer">Hackertours <span class="fas">&#xf35d;</span></a>              
             <a href="join.html">Mitmachen</a>
             <a href="venue.html">Lageplan</a>
             <a href="recap.html">Rückblick</a>