fixed phpdoc (closes symfony/class-loader#3)

Author: Grummfy

src/Symfony/Component/ClassLoader/ClassLoader.php

@@ -19,8 +19,8 @@
  *     $loader = new ClassLoader();
  *
  *     // register classes with namespaces
- *     $loader->add('Symfony\Component', __DIR__.'/component');
- *     $loader->add('Symfony',           __DIR__.'/framework');
+ *     $loader->addPrefix('Symfony\Component', __DIR__.'/component');
+ *     $loader->addPrefix('Symfony',           __DIR__.'/framework');
  *
  *     // activate the autoloader
  *     $loader->register();