minor #12627 Update simple-example.rst (noniagriconomie)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes #12627).

Discussion
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Update simple-example.rst

Minor improvement
The inclusion of the css/js is mainly because of the `parent` call, not only the `include/extend`

Commits
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8a06972 Update simple-example.rst

Author: OskarStark

frontend/encore/simple-example.rst

@@ -269,7 +269,8 @@ you need them:
     + {% endblock %}
 
 Now, the checkout page will contain all the JavaScript and CSS for the ``app`` entry
-(because this is included in ``base.html.twig``) *and* your ``checkout`` entry.
+(because this is included in ``base.html.twig`` and there is the ``{{ parent() }}`` call)
+*and* your ``checkout`` entry.
 
 See :doc:`/frontend/encore/page-specific-assets` for more details. To avoid duplicating
 the same code in different entry files, see :doc:`/frontend/encore/split-chunks`.