Update README.md

Author: BertrandGouny

README.md

@@ -83,6 +83,9 @@ simply mount this directories as a volume to `/var/lib/ldap` and `/etc/ldap/slap
 	-v /data/slapd/config:/etc/ldap/slapd.d
 	-d osixia/openldap
 
+You can also use data volume containers. Please refer to :
+> [https://docs.docker.com/userguide/dockervolumes/](https://docs.docker.com/userguide/dockervolumes/)
+
 ### Using TLS
 
 #### Use autogenerated certificate