Update footer

Author: seanmitchell

_includes/footer.html

@@ -4,6 +4,7 @@
     <ul>
       <li><a href="https://basecamp.com" target="_blank" rel="noopener"><img src="{{ '/assets/images/logo-basecamp.svg' }}" alt="Basecamp"></a></li>
       <li><a href="https://hey.com" target="_blank" rel="noopener"><img src="{{ '/assets/images/logo-hey.svg' }}" alt="HEY"></a></li>
+      <li><a href="https://fizzy.do" target="_blank" rel="noopener"><img src="{{ '/assets/images/logo-fizzy.svg' }}" alt="Fizzy"></a></li>
       <li><a href="https://once.com" target="_blank" rel="noopener"><img src="{{ '/assets/images/logo-once.svg' }}" alt="ONCE"></a></li>
     </ul>
     <p>&copy; {{ 'now' | date: '%Y' }} <a href="https://37signals.com" target="_blank" rel="noopener">37signals</a></p>