fix docs

docs/en/12-taos-sql/24-show.md

@@ -101,6 +101,7 @@ Note: TDengine Enterprise Edition only.
 
 ```sql
 SHOW INDEXES FROM tbl_name [FROM db_name];
+SHOW INDEXES FROM [db_name.]tbl_name;
 ```
 
 Shows indices that have been created.

docs/en/12-taos-sql/27-index.md

@@ -43,6 +43,7 @@ DROP INDEX index_name;
 ````sql
 ```sql
 SHOW INDEXES FROM tbl_name [FROM db_name];
+SHOW INDEXES FROM [db_name.]tbl_name ;
 ````
 
 Shows indices that have been created for the specified database or table.

docs/zh/12-taos-sql/24-show.md

@@ -101,6 +101,7 @@ SHOW GRANTS;
 
 ```sql
 SHOW INDEXES FROM tbl_name [FROM db_name];
+SHOW INDEXES FROM [db_name.]tbl_name;
 ```
 
 显示已创建的索引。

docs/zh/12-taos-sql/27-index.md

@@ -43,6 +43,7 @@ DROP INDEX index_name;
 ````sql
 ```sql
 SHOW INDEXES FROM tbl_name [FROM db_name];
+SHOW INDEXES FROM [db_name.]tbl_name;
 ````
 
 显示在所指定的数据库或表上已创建的索引。