added a note in the documentation about what the C exension does

diff --git a/doc/intro.rst b/doc/intro.rst
index 9a91177..cad60b6 100644 (file)
--- a/doc/intro.rst
+++ b/doc/intro.rst
@@ -102,7 +102,9 @@ Finally, enable the extension in your ``php.ini`` configuration file:
     extension=twig.so
 
 And from now on, Twig will automatically compile your templates to take
-advantage of the C extension.
+advantage of the C extension. Note that this extension does not replace the
+PHP code but only provides an optimized version of the
+``Twig_Template::getAttribute()`` method.
 
 .. tip::