Fix typo in names of roles

config/sample-config2.yaml

@@ -2,8 +2,8 @@
 # groups/users from is done by the membership to ldap_user and
 # ldap_group. These two roles have to be defined manally before
 # pg_ldap_sync can run:
-#     CREATE GROUP ldap_group;
-#     CREATE USER ldap_user;
+#     CREATE GROUP ldap_groups;
+#     CREATE USER ldap_users;
 #
 
 # Connection parameters to LDAP server