docs: add link to function page

Author: kenjis

user_guide_src/source/general/modules.rst

@@ -240,8 +240,9 @@ For Windows:
 Helpers
 =======
 
-Helpers will be automatically discovered within defined namespaces when using the ``helper()`` function, as long as it
-is within the namespaces **Helpers** directory:
+Helpers will be automatically discovered within defined namespaces when using the
+:php:func:`helper()` function, as long as it is within the namespaces **Helpers**
+directory:
 
 .. literalinclude:: modules/009.php