docs: add docs for table level comment (#982)

docs/nightly/en/reference/sql/create.md

@@ -91,6 +91,7 @@ Users can add table options by using `WITH`. The valid options contain the follo
 | `compaction.twcs.time_window` | Compaction time window    | String value, such as '1d' for 1 day. The table usually partitions rows into different time windows by their timestamps. Only available when `compaction.type` is `twcs`.  |
 | `memtable.type` | Type of the memtable.         | String value, supports `time_series`, `partition_tree`. |
 | `append_mode`           | Whether the table is append-only     | String value. Default is 'false', which removes duplicate rows by primary keys and timestamps. Setting it to 'true' to enable append mode and create an append-only table which keeps duplicate rows.     |
+| `comment`           | Table level comment   | String value.      |
 
 #### Create a table with TTL
 For example, to create a table with the storage data TTL(Time-To-Live) is seven days:

docs/nightly/zh/reference/sql/create.md

@@ -92,6 +92,7 @@ CREATE TABLE [IF NOT EXISTS] [db.]table_name
 | `compaction.twcs.time_window` | Compaction 时间窗口    | 字符串值，如 '1d' 表示 1 天。该表会根据时间戳将数据分区到不同的时间窗口中。只在 `compaction.type` 为 `twcs` 时可用 |
 | `memtable.type` | memtable 的类型         | 字符串值，支持 `time_series`，`partition_tree` |
 | `append_mode`           | 该表是否时 append-only 的     | 字符串值. 默认为 'false'，表示会根据主键和时间戳对数据去重。设置为 'true' 可以开启 append 模式和创建 append-only 表，保留所有重复的行     |
+| `comment`           | 表级注释     | 字符串值.      |
 
 #### 创建指定 TTL 的表
 例如，创建一个存储数据 TTL(Time-To-Live) 为七天的表：