minor #13691 [Console] Added a little explaination about Command#interact() (WouterJ)

This PR was squashed before being merged into the 2.3 branch (closes #13691).

Discussion
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[Console] Added a little explaination about Command#interact()

This has confused some long time Symfony users recently: https://twitter.com/jmolivas/status/566283453264850945

| Q             | A
| ------------- | ---
| Fixed tickets | -
| License       | MIT

Commits
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38e7b72 [Console] Added a little explaination about Command#interact()

src/Symfony/Component/Console/Command/Command.php

@@ -175,6 +175,10 @@ class Command
     /**
      * Interacts with the user.
      *
+     * This method is executed before the InputDefinition is validated.
+     * This means that this is the only place where the command can
+     * interactively ask for values of missing required arguments.
+     *
      * @param InputInterface  $input  An InputInterface instance
      * @param OutputInterface $output An OutputInterface instance
      */