issues/20050 Remove Doctrine mappings YML from documentation

#20050

Author: Cosmin Sandu

reference/configuration/doctrine.rst

@@ -269,9 +269,14 @@ you can control. The following configuration options exist for a mapping:
 ........
 
 One of ``annotation`` (for PHP annotations; it's the default value),
-``attribute`` (for PHP attributes), ``xml``, ``yml``, ``php`` or
+``attribute`` (for PHP attributes), ``xml``, ``php`` or
 ``staticphp``. This specifies which type of metadata type your mapping uses.
 
+.. deprecated:: ORM 3.0
+
+    The ``yml`` mapping configuration is deprecated and will be removed in doctrine/orm 3.0.
+
+
 See `Doctrine Metadata Drivers`_ for more information about this option.
 
 ``dir``