Update user_guide_src/source/libraries/caching/014.php

Co-authored-by: Michal Sniatala <michal@sniatala.pl>

Author: ddevsr

user_guide_src/source/libraries/caching/014.php

@@ -12,7 +12,7 @@ class Cache extends BaseConfig
         'host'       => '127.0.0.1',
         'password'   => null,
         'port'       => 6379,
-        'async'      => false,
+        'async'      => false, // specific to Predis and ignored by the native Redis extension
         'persistent' => false,
         'timeout'    => 0,
         'database'   => 0,