fix(accessibility): fix missing alt for img

Error: An img element must have an alt attribute, except under certain conditions.
Source: Nu Html Checker

Author: Rotzbua

_i18n/en.yml

@@ -27,6 +27,7 @@ generic:
   page-not-found-short: "Page not found"
   page-not-found-long: "The requested page could not be found."
   accessibility:
+    section-menu: "Section menu"
     lang-menu: "Language switcher"
     copy: "Copy link"
     copied: "Link copied!"

_includes/nav.html

@@ -51,8 +51,9 @@
           </div>
         </div>
 
-        <button class="navbar-toggler" onclick="openNav()"><img
-                src="{{ site.baseurl_root }}/assets/images/icons/burger.svg" /></button>
+        <button class="navbar-toggler" onclick="openNav()">
+          <img src="{{ site.baseurl_root }}/assets/images/icons/burger.svg" alt="{% t generic.accessibility.section-menu %}">
+        </button>
       </div>
 
     </div>