Add Copyright mark

src/App.vue

@@ -8,6 +8,12 @@
       <router-link to="/nordmensa/heute">Nordmensa</router-link>
     </nav>
     <router-view></router-view>
+
+    <footer>
+      <hr>
+      Developed by <a href="https://webschneider.org">webschneider.org</a>
+      &copy; {{ new Date().getFullYear() }}
+    </footer>
   </div>
 </template>
 
@@ -34,4 +40,7 @@ export default {
   max-width: 30em;
   margin: 0 auto;
 }
+footer{
+  margin: 1em 0;
+}
 </style>