Show arxiv as paper title link in case no other link is present

Author: OliEfr

_includes/section.html

@@ -21,6 +21,8 @@
       {%assign title_link = publication.webpage %}
       {%elsif publication.paper%}
       {%assign title_link = publication.paper %}
+      {%elsif publication.arxiv%}
+      {%assign title_link = publication.arxiv %}
       {%else%}
       {%assign title_link =  '' %}
       {%endif%}
@@ -93,4 +95,4 @@ <h3 class="publication-title"><a class="{% if title_link == '' %}disable-link{%
       </div>
     </div>
   </div>
-</div>
+</div>