feature symfony#4966 [symfony#4231] Clarify that only the main command triggers events (riperez)

This PR was merged into the 2.3 branch.

Discussion
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[symfony#4231] Clarify that only the main command triggers events

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | symfony#4231

Commits
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3f5ce4d [symfony#4231] Clarify that only the main command triggers events

Author: weaverryan

components/console/events.rst

@@ -20,6 +20,11 @@ the wheel, it uses the Symfony EventDispatcher component to do the work::
     $application->setDispatcher($dispatcher);
     $application->run();
 
+.. caution::
+
+    Console events are only triggered by the main command being executed.
+    Commands called by the main command will not trigger any event.
+
 The ``ConsoleEvents::COMMAND`` Event
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