add text alternative to social links for #602

src/templates/partials/social-links.twig

@@ -7,6 +7,7 @@
             name: name,
             class: large ? 'f5' : null
           } %}
+          <span class="sr-only">Link to page/content on {{name}}</span>
         </a>
       </li>
     {% endif %}