Fix typo.

git-svn-id: http://root.cern.ch/svn/root/trunk@21423 27541ba8-7e3a-0410-8455-c3a389f83636

xml/doc/index.txt

@@ -2,7 +2,7 @@ This directory contains all classes, related to the ROOT xml file implementation
 BEGIN_HTML
  See:
 <ul>
-<li> Main functionality of ROOT xml documentaed in TXMLFile class </li>
+<li> Main functionality of ROOT xml documented in TXMLFile class </li>
 <li> Special xml parser for ROOT xml files implemented in TXMLEngine class </li>
 <li><a href="ftp://root.cern.ch/root/doc/11InputOutput.pdf">Some documentation can be found in the end of the Input/Output chapter
     </a></li>