minor #20182 [Translation] fix: add nikic/php-parser requirement for translation:extract in tran… (bsramin)

This PR was submitted for the 7.1 branch but it was squashed and merged into the 6.4 branch instead.

Discussion
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[Translation] fix: add nikic/php-parser requirement for translation:extract in tran…

…slation.rst

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9041d05 [Translation] fix: add nikic/php-parser requirement for translation:extract in tran…

Author: javiereguiluz

translation.rst

@@ -462,6 +462,14 @@ The ``translation:extract`` command looks for missing translations in:
     The support of PHP files/classes that use constraint attributes was
     introduced in Symfony 6.2.
 
+To read PHP files, is used the new ``PhpAstExtractor`` service supports all kinds of ``trans()`` function calls, usages of :class:`Symfony\\Component\\Translation\\TranslatableMessage` class, messages defined in validation constraints, etc...
+
+To use the new translation extractor, install the ``nikic/php-parser`` package using Composer, before using `translation:extract`.
+
+.. code-block:: terminal
+
+    $ composer require nikic/php-parser
+
 .. _translation-resource-locations:
 
 Translation Resource/File Names and Locations