volunteers: minor UI improvement

cfp/templates/cfp/staff/volunteer_list.html

@@ -47,7 +47,7 @@
                 {% if volunteer.notes %}<span class="glyphicon glyphicon-envelope pull-right" data-toggle="tooltip" data-placement="bottom" title="{% trans "The volunteer made a few remarks to the staff." %}"></span>{% endif %}
             </td>
             <td>{{ volunteer.email }}</td>
-            <td>{{ volunteer.phone_number }}</td>
+            <td><a href="tel:{{ volunteer.phone_number }}">{{ volunteer.phone_number }}</a>{% if volunteer.sms_prefered %} (SMS){% endif %}</td>
             <td>
                 {% for activity in volunteer.activities.all %}
                 <span class="badge">{{ activity }}</span>