Add versionadded

Author: ker0x

reference/constraints/UniqueEntity.rst

@@ -556,6 +556,10 @@ this option to specify one or more fields to only ignore ``null`` values on them
 
 **type**: ``array`` **default**: ``[]``
 
+.. versionadded:: 7.1
+
+    The ``identifierFieldNames`` option was introduced in Symfony 7.1.
+
 The ``identifierFieldNames`` option allows you to specify the field
 (or list of fields) used to identify a Doctrine entity, set by the
 `entityClass`_ option, when you use a PHP class to update it.