add Untappd logo (https://untappd.com/)

index.html

@@ -270,6 +270,11 @@
             <img class="icon" src="images/icons/whatsapp.svg" alt="WhatsApp Logo">WhatsApp</a>
         <br>
 
+        <!-- Untappd -->
+        <a class="button button-untappd" href="#" target="_blank" rel="noopener">
+            <img class="icon" src="images/icons/untappd.svg" alt="Untappd Logo">Untappd</a>
+        <br>
+
         <!-- Wordpress -->
         <a class="button button-wordpress" href="#" target="_blank" rel="noopener">
             <img class="icon" src="images/icons/wordpress.svg" alt="Wordpress Logo">Wordpress</a>