Document PSR-0 and PSR-4 as two supported PSRs

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

developer_manual/digging_deeper/psr.rst

@@ -6,6 +6,13 @@ PSR
 
 On this page you find information about the implemented `php standards recommendations <https://www.php-fig.org/psr/>`_ in Nextcloud.
 
+.. _psr0:
+
+PSR-0: Autoloading
+------------------
+
+This standard has been deprecated and will be removed from Nextcloud. Please see the :ref:`PSR-4 section<psr4>` instead.
+
 .. _psr3:
 
 PSR-3: Logger Interface
@@ -13,6 +20,13 @@ PSR-3: Logger Interface
 
 As of Nextcloud 19, the dependency injection container can inject an instance of a ``\Psr\Log\LoggerInterface``. This is merely a wrapper of the existing (and strongly typed) ``\OCP\ILogger``. Apps may still use the Nextcloud logger, but the `PSR-3`_ implementation shall easy the integration of 3rd party libraries that require the `PSR-3`_ logger.
 
+.. _psr4:
+
+PSR-4: Autoloading
+------------------
+
+The `PSR-4` standard describes how class files should be named, so Nextcloud can automatically load them. See the :ref:`classloader docs<appclassloader>` for details.
+
 .. _psr11:
 
 PSR-11: Container Interface
@@ -20,5 +34,7 @@ PSR-11: Container Interface
 
 As of Nextcloud 20, the dependency injection container follows the `PSR-11`_ container interface, so you may start type-hinting ``\Psr\Container\ContainerInterface`` whenever you want an instance of a container and use ``has($id)`` to check for existance and ``get($id)`` to retrieve an instance of a service. See the :ref:`dependency injection docs <dependency-injection>` for details.
 
+.. _`PSR-0`: https://www.php-fig.org/psr/psr-0/
 .. _`PSR-3`: https://www.php-fig.org/psr/psr-3/
+.. _`PSR-4`: https://www.php-fig.org/psr/psr-4/
 .. _`PSR-11`: https://www.php-fig.org/psr/psr-11/