fix ddlchekcer-readme (pingcap#127)

Author: LeopPro

ddl_checker/README.md

@@ -42,13 +42,13 @@ SETMOD usage: SETMOD <MODCODE>; MODCODE = ["Auto", "Prompt", "Offline"] (case in
 [DDLChecker] SQL execution succeeded
 
 [Auto] > SETMOD PROMPT;
-[Query] > ALTER TABLE table_name MODIFY column_1 int(11) NOT NULL;
+[Prompt] > ALTER TABLE table_name MODIFY column_1 int(11) NOT NULL;
 [DDLChecker] Do you want to synchronize table [table_name] from MySQL and drop table [] in ExecutableChecker?(Y/N)y
 [DDLChecker] Syncing Table table_name
 [DDLChecker] SQL execution succeeded
 
-[Query] > setmod manual;
-[Manual] > ALTER TABLE table_name MODIFY column_1 int(11) NOT NULL;
+[Prompt] > setmod offline;
+[Offline] > ALTER TABLE table_name MODIFY column_1 int(11) NOT NULL;
 [DDLChecker] SQL execution failed: [schema:1146]Table 'test.table_name' doesn't exist
 
 ```