Add link to Merch store in top navigation bar

Author: germainelee

layouts/partials/header/header.html

@@ -34,6 +34,9 @@
           <li class="nav-item">
             <a class="nav-link" href="https://directory.owncast.online" target="_blank" rel="noopener noreferrer">Directory</a>
           </li>
+          <li class="nav-item">
+            <a class="nav-link" href="https://merch.owncast.online" target="_blank" rel="noopener noreferrer">Shop</a>
+          </li>
       </ul>
       <div class="break order-6 d-md-none"></div>
       <form class="navbar-form flex-grow-1 order-7 order-md-3">