Added PSR-4 ClassLoader to list

Author: dosten

components/class_loader/introduction.rst

@@ -12,11 +12,14 @@ Usage
 
 Whenever you reference a class that has not been required or included yet,
 PHP uses the `autoloading mechanism`_ to delegate the loading of a file defining
-the class. Symfony2 provides two autoloaders, which are able to load your classes:
+the class. Symfony2 provides three autoloaders, which are able to load your classes:
 
 * :doc:`/components/class_loader/class_loader`: loads classes that follow
   the `PSR-0` class naming standard;
 
+* :doc:`/components/class_loader/psr4_class_loader`: loads classes that follow
+  the `PSR-4` class naming standard;
+
 * :doc:`/components/class_loader/map_class_loader`: loads classes using
   a static map from class name to file path.