minor #20951 [Twig] [TwigBundle] Describe the new behaviour of twig.cache config (Okhoshi)

This PR was merged into the 7.3 branch.

Discussion
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[Twig] [TwigBundle] Describe the new behaviour of twig.cache config

Update the description of the `twig.cache` config to follow the changes implemented in symfony/symfony#54384.

Fixes #20948

cc `@alexandre`-daubois

Commits
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8c5f22b [TwigBundle] Describe the new behaviour of twig.cache config

Author: javiereguiluz

reference/configuration/twig.rst

@@ -71,7 +71,7 @@ application harder to maintain.
 cache
 ~~~~~
 
-**type**: ``string`` | ``false`` **default**: ``%kernel.cache_dir%/twig``
+**type**: ``string`` | ``boolean`` **default**: ``true``
 
 Before using the Twig templates to render some contents, they are compiled into
 regular PHP code. Compilation is a costly process, so the result is cached in
@@ -82,6 +82,16 @@ is not recommended; not even in the ``dev`` environment, because the
 ``auto_reload`` option ensures that cached templates which have changed get
 compiled again.
 
+Specify the path where the cache should be stored. If set to ``true``, the cache
+defaults to ``%kernel.cache_dir%/twig``. However, if the ``auto_reload`` option is
+disabled and ``%kernel.build_dir%`` is different from ``%kernel.cache_dir%``,
+the cache will instead be stored in ``%kernel.build_dir%/twig``.
+
+.. versionadded:: 7.3
+
+    Support for ``true`` value was added in Symfony 7.3, and it became the default
+    value for this option instead of ``%kernel.cache_dir%/twig``.
+
 charset
 ~~~~~~~