minor symfony#24110 [Form] Add help description to debug:form command (yceruto)

This PR was merged into the 3.4 branch.

Discussion
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[Form] Add help description to debug:form command

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

I forgot to add this one in the introduction of the command.

Commits
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f8afe02 Add help description to debug:form command

Author: fabpot

src/Symfony/Component/Form/Command/DebugCommand.php

@@ -51,6 +51,16 @@ protected function configure()
                 new InputOption('format', null, InputOption::VALUE_REQUIRED, 'The output format (txt or json)', 'txt'),
             ))
             ->setDescription('Displays form type information')
+            ->setHelp(<<<'EOF'
+The <info>%command.name%</info> command displays information about a form type.
+
+Either the fully-qualified class name or the short class name can be used:
+
+  <info>php %command.full_name% Symfony\Component\Form\Extension\Core\Type\ChoiceType</info>
+  <info>php %command.full_name% ChoiceType</info>
+
+EOF
+            )
         ;
     }