docs: add note

Author: kenjis

user_guide_src/source/general/common_functions.rst

@@ -331,6 +331,8 @@ Miscellaneous Functions
     :param   string  $method: The named route alias, or name of the controller/method to match.
     :param   mixed   $params: One or more parameters to be passed to be matched in the route.
 
+    .. note:: This function requires the controller/method to have a route defined in **app/Config/routes.php**.
+
     Generates a URI relative to the domain name (not **baseUrl**) for you based on either a named route alias,
     or a controller::method combination. Will take parameters into effect, if provided.
 

user_guide_src/source/helpers/url_helper.rst

@@ -351,6 +351,8 @@ The following functions are available:
     :returns: Absolute URL
     :rtype: string
 
+    .. note:: This function requires the controller/method to have a route defined in **app/Config/routes.php**.
+
     Builds an absolute URL to a controller method in your app. Example:
 
     .. literalinclude:: url_helper/021.php