Exclude sponsor logos from blanket CC BY-SA statement

closes #266

Author: AndrewKvalheim

_layouts/sponsors.html

@@ -51,9 +51,11 @@ <h2>{{ level[1] }}</h2>
   <hr>
 {% endfor %}
 
-<ul class="nav nav-pills nav-pills-centered" style="margin-top: 3em;">
+<ul class="nav nav-pills nav-pills-centered" style="margin-bottom: 2em;margin-top: 3em;">
   {% for sponsor_year in site.sponsor-years %}
   {% capture y %}{{ sponsor_year.slug }}{% endcapture %}{% assign y = y | plus: 0 %}
   <li class="{% if y == year %}active{% endif %}"><a href="{{ sponsor_year.url }}">{{ y }}</a></li>
   {% endfor %}
 </ul>
+
+<p class="text-center text-muted">Logos are used with permission on this site and are not licensed by SeaGL.</p>