Add something about clear the cache when template is added

Author: ip512

book/templating.rst

@@ -1012,6 +1012,11 @@ from the bundle to ``app/Resources/AcmeBlogBundle/views/Blog/index.html.twig``
 (the ``app/Resources/AcmeBlogBundle`` directory won't exist, so you'll need
 to create it). You're now free to customize the template.
 
+When Symfony looks into folders to discover templates, the location of the 
+found template is cached. If you add a template in a new location, don't 
+forget to clear the cache (``./app/console cache:clear``), even if you are in 
+debug mode.
+
 This logic also applies to base bundle templates. Suppose also that each
 template in ``AcmeBlogBundle`` inherits from a base template called
 ``AcmeBlogBundle::layout.html.twig``. Just as before, Symfony2 will look in