add v600 doc directories.

git-svn-id: http://root.cern.ch/svn/root/trunk@44195 27541ba8-7e3a-0410-8455-c3a389f83636

tree/doc/v600/index.html

+<br/> 
+<hr/> 
+<a name="tree"></a> 
+<h3>Tree Libraries</h3>

tutorials/doc/v600/index.html

+<br/> 
+<hr/> 
+<a name="tutorials"></a> 
+<h3>Tutorials</h3>