Use versionadded instead of note directive

Author: OskarStark

components/cache/adapters/chain_adapter.rst

@@ -58,10 +58,10 @@ incompatible adapters are silently ignored::
         new FilesystemAdapter(),  // DOES implement PruneableInterface
     ]);
 
-    // prune will proxy the call to FilesystemAdapter while silently skipping ApcuAdapter
+    // prune will proxy the call to FilesystemAdapter while silently skip ApcuAdapter
     $cache->prune();
 
-.. note::
+.. versionadded:: 3.4
 
     Since Symfony 3.4, this adapter implements :class:`Symfony\\Component\\Cache\\PruneableInterface`,
     allowing for manual :ref:`pruning of expired cache entries <component-cache-cache-pool-prune>` by