add privacy notice link to footer

_includes/footer.html

 <footer class="site-footer">
-  <p>&copy; {{ site.time | date: "%Y" }} {{ site.copyright }}</p>
+  <p>&copy; {{ site.time | date: "%Y" }} {{ site.copyright }}<br />
+  <a href="https://www.imperial.ac.uk/about-the-site/privacy/">Privacy Notice</a></p>
 </footer>