docs: add ttl/comment spec for 'alter table'

docs/en/12-taos-sql/03-table.md

@@ -25,7 +25,7 @@ create_definition:
     col_name column_definition
 
 column_definition:
-    type_name [comment 'string_value'] [PRIMARY KEY] [ENCODE 'encode_type'] [COMPRESS 'compress_type'] [LEVEL 'level_type'] 
+    type_name [comment 'string_value'] [PRIMARY KEY] [ENCODE 'encode_type'] [COMPRESS 'compress_type'] [LEVEL 'level_type']
 
 table_options:
     table_option ...
@@ -136,6 +136,18 @@ ALTER TABLE tb_name MODIFY COLUMN field_name data_type(length);
 ALTER TABLE tb_name RENAME COLUMN old_col_name new_col_name
 ```
 
+### Alter Table TTL
+
+```sql
+ALTER TABLE tb_name TTL value
+```
+
+### Alter Table Comment
+
+```sql
+ALTER TABLE tb_name COMMENT 'string_value'
+```
+
 ## Modify a Subtable
 
 ```sql
@@ -165,6 +177,18 @@ alter_table_option: {
 ALTER TABLE tb_name SET TAG tag_name=new_tag_value;
 ```
 
+### Alter Table TTL
+
+```sql
+ALTER TABLE tb_name TTL value
+```
+
+### Alter Table Comment
+
+```sql
+ALTER TABLE tb_name COMMENT 'string_value'
+```
+
 ## Delete a Table
 
 The following SQL statement deletes one or more tables.

docs/zh/12-taos-sql/03-table.md

@@ -23,10 +23,10 @@ create_subtable_clause: {
 }
 
 create_definition:
-    col_name column_definition 
+    col_name column_definition
 
 column_definition:
-    type_name [comment 'string_value'] [PRIMARY KEY] [ENCODE 'encode_type'] [COMPRESS 'compress_type'] [LEVEL 'level_type'] 
+    type_name [comment 'string_value'] [PRIMARY KEY] [ENCODE 'encode_type'] [COMPRESS 'compress_type'] [LEVEL 'level_type']
 
 table_options:
     table_option ...
@@ -136,6 +136,18 @@ ALTER TABLE tb_name MODIFY COLUMN field_name data_type(length);
 ALTER TABLE tb_name RENAME COLUMN old_col_name new_col_name
 ```
 
+### 修改表生命周期
+
+```sql
+ALTER TABLE tb_name TTL value
+```
+
+### 修改表注释
+
+```sql
+ALTER TABLE tb_name COMMENT 'string_value'
+```
+
 ## 修改子表
 
 ```sql
@@ -165,6 +177,18 @@ alter_table_option: {
 ALTER TABLE tb_name SET TAG tag_name=new_tag_value;
 ```
 
+### 修改表生命周期
+
+```sql
+ALTER TABLE tb_name TTL value
+```
+
+### 修改表注释
+
+```sql
+ALTER TABLE tb_name COMMENT 'string_value'
+```
+
 ## 删除表
 
 可以在一条 SQL 语句中删除一个或多个普通表或子表。