Add link to software license key FAQ.

Author: kleinerm

_layouts/default.html

@@ -43,6 +43,7 @@ <h1><a href="/">Psychtoolbox-3</a></h1>
       <li><a href=https://www.psychtoolbox.net/license-key>Paid Support</a></li>
       <li><a href={{ site.baseurl }}/forum.html>Community Forum</a></li>
       <li><a href=https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ>FAQ</a></li>
+      <li><a href=https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ#faqs-for-software-license-keys>Software License keys FAQ</a></li>
     </ul>
   </li>
   </ul>