Add missing versionadded directive. refs #11748

Author: OskarStark

components/cache/adapters/couchbasebucket_adapter.rst

@@ -7,6 +7,10 @@
 Couchbase Cache Adapter
 =======================
 
+.. versionadded:: 5.1
+
+    The CouchbaseBucketAdapter was introduced in Symfony 5.1.
+
 This adapter stores the values in-memory using one (or more) `Couchbase server`_
 instances. Unlike the :ref:`APCu adapter <apcu-adapter>`, and similarly to the
 :ref:`Memcached adapter <memcached-adapter>`, it is not limited to the current server's