Fix one more wrong doc link

git-svn-id: http://root.cern.ch/svn/root/trunk@21354 27541ba8-7e3a-0410-8455-c3a389f83636

vmc/doc/index.txt

@@ -8,7 +8,7 @@ BEGIN_HTML
     </a></li>
 <li><a href="http://root.cern.ch/root/vmc/Geant4VMC.html">the Geant4 Virtual Monte Carlo
     </a></li>
-<li><a href="http://root.cern.ch/root/vmc/HowtoMC.html">How to use ROOT with Monte Carlo programs like Geant3, Geant4
+<li><a href="http://root.cern.ch/root/HowtoMC.html">How to use ROOT with Monte Carlo programs like Geant3, Geant4
     </a></li>
 <li><a href="http://aliceinfo.cern.ch/Offline">The ALICE Offline Project
       </A></li>