upgrade/5.8.x-to-6.0.0.md: sql statements to change size for htable columns

docs/install/upgrade/5.8.x-to-6.0.0.md

@@ -56,5 +56,6 @@ Run following SQL statements in MySQL client to upgrade database
 structure from v5.8 to v6.0:
 
 ``` sql
-...
+ALTER TABLE htable CHANGE COLUMN `key_name` `key_name` VARCHAR(256) DEFAULT '' NOT NULL; -- # was VARCHAR(64) DEFAULT '' NOT NULL
+ALTER TABLE htable CHANGE COLUMN `key_value` `key_value` VARCHAR(512) DEFAULT '' NOT NULL; -- # was VARCHAR(128) DEFAULT '' NOT NULL
 ```