docs: add slow log descriptions

docs/en/14-reference/12-config/index.md

@@ -443,6 +443,26 @@ The charset that takes effect is UTF-8.
 | Default Value | 0                                                                                                                                           |
 | Note          | When it's bigger than 0, the log file would be renamed to "taosdlog.xxx" in which "xxx" is the timestamp when the file is changed last time |
 
+### slowLogThreshold
+
+| Attribute     | Description                                                                                              |
+| ------------- | -------------------------------------------------------------------------------------------------------- |
+| Applicable    | Client only                                                                                              |
+| Meaning       | When an operation execution time exceeds this threshold, the operation will be logged in slow log file   |
+| Unit          | second                                                                                                   |
+| Default Value | 3                                                                                                        |
+| Note          | All slow operations will be logged in file "taosSlowLog" in the log directory                            |
+
+### slowLogScope
+
+| Attribute       | Description                                                             |
+| --------------- | ----------------------------------------------------------------------- |
+| Applicable      | Client only                                                             |
+| Meaning         | Slow log type to be logged                                              |
+| Optional Values | ALL, QUERY, INSERT, OTHERS, NONE                                        |
+| Default Value   | ALL                                                                     |
+| Note            | All slow operations will be logged by default, one option could be set  |
+
 ### debugFlag
 
 | Attribute     | Description                                               |

docs/zh/14-reference/12-config/index.md

@@ -461,6 +461,26 @@ charset 的有效值是 UTF-8。
 | 缺省值   | 0                                                                                   |
 | 补充说明 | 大于 0 时，日志文件会被重命名为 taosdlog.xxx，其中 xxx 为日志文件最后修改的时间戳。 |
 
+### slowLogThreshold
+
+| 属性     | 说明                                                          |
+| -------- | ------------------------------------------------------------- |
+| 适用范围 | 仅客户端适用                                                  |
+| 含义     | 指定慢查询门限值，大于等于门限值认为是慢查询                  |
+| 单位     | 秒                                                            |
+| 缺省值   | 3                                                             |
+| 补充说明 | 每个客户端中所有慢查询会被记录在日志目录下的taosSlowLog文件中 |
+
+### slowLogScope
+
+| 属性     | 说明                                                          |
+| -------- | --------------------------------------------------------------|
+| 适用范围 | 仅客户端适用                                                  |
+| 含义     | 指定启动记录哪些类型的慢查询                                  |
+| 可选值   | ALL, QUERY, INSERT, OTHERS, NONE                              |
+| 缺省值   | ALL                                                           |
+| 补充说明 | 默认记录所有类型的慢查询，可通过配置只记录某一类型的慢查询    |
+
 ### debugFlag
 
 | 属性     | 说明                                                                                              |