social/social_media_xing/views/website_templates.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
  <data>

    <template id="footer_default_extra"
              inherit_id="website.footer_default">
      <xpath expr="//a[6]"
             position="after">

        <a t-att-href="website.social_xing"
           t-if="website.social_xing">
          <i class="fa fa-xing"/>
        </a>

      </xpath>
    </template>

  </data>
</openerp>