minor #16829 Add assets to the documentation (tacman)

This PR was squashed before being merged into the 6.1 branch.

Discussion
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Add assets to the documentation

'assets' used to be in the /Resources folder, but seems like it should be at the root now, like config and views/templates.

I'm guessing that if package.json is in right place, then flex will register the stimulus controller, although I haven't been able to do that yet: symfony/flex#919

Commits
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32ff705 Add assets to the documentation

Author: javiereguiluz

bundles.rst

@@ -98,6 +98,9 @@ to be adjusted if needed:
 ``src/``
     Contains all PHP classes related to the bundle logic (e.g. ``Controller/RandomController.php``).
 
+``assets/``
+    Contains javascript, css, images and other assets related to the bundle that are not in ``/public`` (e.g. stimulus controllers)
+    
 ``config/``
     Houses configuration, including routing configuration (e.g. ``routing.yaml``).