Add memcached unis socket instructions

config/config.sample.php

@@ -1355,7 +1355,8 @@ $CONFIG = [
  * Server details for one or more memcached servers to use for memory caching.
  */
 'memcached_servers' => [
-	// hostname, port and optional weight. Also see:
+	// hostname, port and optional weight
+	// or path and port 0 for unix socket. Also see:
 	// https://www.php.net/manual/en/memcached.addservers.php
 	// https://www.php.net/manual/en/memcached.addserver.php
 	['localhost', 11211],