docs: improve references

Author: kenjis

user_guide_src/source/general/configuration.rst

@@ -288,7 +288,7 @@ There are two ways to implement a Registrar: implicit and explicit.
 Implicit Registrars
 ===================
 
-Any namespace may define registrars by using the **Config/Registrar.php** file, if discovery
+Any namespace may define registrars by using the **Config/Registrar.php** file, if :ref:`auto-discovery`
 is enabled in :doc:`Modules </general/modules>`. These files are classes whose methods are
 named for each configuration class you wish to extend. For example, a third-party module might
 wish to supply an additional template to ``Pager`` without overwriting whatever a develop has

user_guide_src/source/general/modules.rst

@@ -73,6 +73,8 @@ your classes. All we need to do is provide the list of paths to those files and
 
 .. literalinclude:: modules/002.php
 
+.. _auto-discovery:
+
 **************
 Auto-Discovery
 **************
@@ -83,7 +85,7 @@ file types, including:
 
 - :doc:`Events <../extending/events>`
 - :doc:`Filters <../incoming/filters>`
-- :doc:`Registrars <./configuration>`
+- :ref:`registrars`
 - :doc:`Route files <../incoming/routing>`
 - :doc:`Services <../concepts/services>`