minor #9879 Add link to configuration documentation (dhaaker)

This PR was submitted for the 4.1 branch but it was merged into the 3.4 branch instead (closes #9879).

Discussion
----------

Add link to configuration documentation

The link is missing from the fundamentals listing.

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/roadmap for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `master` for features of unreleased versions).

-->

Commits
-------

b4761a3 Add link to configuration documentation

Author: javiereguiluz

page_creation.rst

@@ -240,6 +240,7 @@ Ok, time to finish mastering the fundamentals by reading these articles:
 * :doc:`/routing`
 * :doc:`/controller`
 * :doc:`/templating`
+* :doc:`/configuration`
 
 Then, learn about other important topics like the
 :doc:`service container </service_container>`,