minor #34887 [FrameworkBundle] Add info & example to auto_mapping config (ogizanagi)

This PR was merged into the 4.3 branch.

Discussion
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[FrameworkBundle] Add info & example to auto_mapping config

| Q             | A
| ------------- | ---
| Branch?       | 4.3 <!-- see below -->
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | N/A <!-- prefix each issue number with "Fix #", if any -->
| License       | MIT
| Doc PR        | N/A

Backport part of #34707 and add example.

Commits
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8eb29a7b73 [FrameworkBundle] Add info & example to auto_mapping config

Author: fabpot

DependencyInjection/Configuration.php

@@ -855,6 +855,11 @@ private function addValidationSection(ArrayNodeDefinition $rootNode)
                             ->end()
                         ->end()
                         ->arrayNode('auto_mapping')
+                            ->info('A collection of namespaces for which auto-mapping will be enabled.')
+                            ->example([
+                                'App\\Entity\\' => [],
+                                'App\\WithSpecificLoaders\\' => ['validator.property_info_loader'],
+                            ])
                             ->useAttributeAsKey('namespace')
                             ->normalizeKeys(false)
                             ->beforeNormalization()