-fix documentation links

doc/index.html

@@ -26,8 +26,8 @@
 
     <ul>
       <li><a href="/handbook/gnunet.html">GNUnet Reference Manual</li>
-      <li><a href="/tutorial/gnunet-tutorial.html">GNUnet C Tutorial</li>
-      <li><a href="/doxygen/">GNUnet Doxygen</li>
+      <li><a href="/tutorial/tutorial.html">GNUnet C Tutorial</li>
+      <li><a href="/doxygen/html">GNUnet Doxygen</li>
       <li><a href="https://rest.gnunet.org/">REST API</a></li>
       <li><a href="https://bib.gnunet.org/">Bibliography</a></li>
     </ul>