Edit tutorial url

Author: mdiazmel

README.md

@@ -23,7 +23,7 @@
 
 <p align="center">
   <a href="https://clinicadl.readthedocs.io/">Documentation</a> |
-  <a href="https://aramislab.paris.inria.fr/clinicadl/tuto/intro.html">Tutorial</a> |
+  <a href="https://aramislab.paris.inria.fr/clinicadl/tuto">Tutorial</a> |
   <a href="https://groups.google.com/forum/#!forum/clinica-user">Forum</a>
 </p>