minor #10018 [Messenger] Added a learn more section (Nyholm, javiereguiluz)

This PR was submitted for the master branch but it was merged into the 4.1 branch instead (closes #10018).

Discussion
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[Messenger] Added a learn more section

There should be a link from the [component page](https://symfony.com/doc/current/components/messenger.html) to the [How to use Messenger page](https://symfony.com/doc/current/messenger.html)

Commits
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7faacfb Added a note about using the component in Symfony apps
07c3b43 Added a learn more section

Author: javiereguiluz

components/messenger.rst

@@ -11,6 +11,12 @@ The Messenger Component
     The component is greatly inspired by Matthias Noback's series of `blog posts
     about command buses`_ and the `SimpleBus project`_.
 
+.. seealso::
+
+    This article explains how to use the Messenger features as an independent
+    component in any PHP application. Read the :doc:`/messenger` article to
+    learn about how to use it in Symfony applications.
+
 Installation
 ------------
 
@@ -195,6 +201,14 @@ It will wrap the received messages into ``ReceivedMessage`` objects and the
 ``SendMessageMiddleware`` middleware will know it should not route these
 messages again to a transport.
 
+Learn More
+----------
+
+.. toctree::
+    :maxdepth: 1
+    :glob:
+
+    /messenger/*
 
 .. _blog posts about command buses: https://matthiasnoback.nl/tags/command%20bus/
 .. _SimpleBus project: http://simplebus.io