show fahrplan link on landing page

src/plainui/jinja2/plainui/landing.html

@@ -75,7 +75,16 @@
                 {{ _("login") }}
             </a>
         </div>
-
+        <div class="text-center m-3">
+            <a
+                href="{{ url('plainui:public_fahrplan' ) }}"
+                title="{{ _("fahrplan") }}"
+                class="rc3-header-link p-2"
+                target="_blank"
+            >
+                {{ _("fahrplan") }}
+            </a>
+        </div>
         <div class="text-center m-3">
             <a
                 href="https://tickets.events.ccc.de/RC3-21/"