License added to the xml documentation files

[SVN r34894]

string/doc/intro.xml

@@ -1,6 +1,12 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
 "http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
+
+<!-- Copyright (c) 2002-2006 Pavol Droba.
+     Subject to the Boost Software License, Version 1.0. 
+     (See accompanying file LICENSE-1.0 or  http://www.boost.org/LICENSE-1.0)
+-->
+
 <section id="string_algo.intro" last-revision="$Date$">
     <title>Introduction</title>