minor symfony#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 symfony#9879).

Discussion
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Add link to configuration documentation

The link is missing from the fundamentals listing.

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Commits
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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>`,