Add verisonAdded

Author: jderusse

components/lock.rst

@@ -223,6 +223,9 @@ support blocking, and expects a TTL to avoid stalled locks::
 PdoStore
 ~~~~~~~~
 
+.. versionadded:: 4.2
+    The PdoStore was introduced Symfony 4.2.
+
 
 The PdoStore saves locks in an SQL database, it requires a `PDO`_,
 `Doctrine DBAL Connection`_, or `Data Source Name (DSN)`_. This store does not