docs: csv encode format

docs/en/openmldb_sql/dml/LOAD_DATA_STATEMENT.md

@@ -201,6 +201,10 @@ Importing supports two data formats: CSV and Parquet. Special attention should b
    2. Dates cannot be in the `yyyy-MM-dd HH:mm:ss` format; for instance, `2022-2-2 00:00:00` will result in a parsing error.
 5. Local mode does not support quote escaping for strings. If your strings contain quote characters, it is recommended to use the cluster mode.
 6. If cluster mode encounters parsing failures during CSV reading, the failed column values are set to NULL, and the import process continues. In local mode, parsing failures result in direct errors, and the import is not continued.
+7. It is recommended to use UTF-8 as the encoding format for CSV. Chinese character encodings like GB are not supported. If the Chinese characters in the table data are displayed as garbled after CSV import, please convert the format of the CSV source data before importing. You can refer to the following command:
+   ```bash
+   iconv -f GBK -t UTF-8 gbk.csv > utf8.csv
+   ```
 
 ## PutIfAbsent Explanation
 

docs/zh/openmldb_sql/dml/LOAD_DATA_STATEMENT.md

@@ -200,6 +200,10 @@ curl http://<ns_endpoint>/NameServer/UpdateOfflineTableInfo -d '{"db":"<db_name>
 	2. date不可以是年月日时分秒，例如`2022-2-2 00:00:00`将解析失败。
 5. local的字符串不支持quote转义，所以如果你的字符串中存在quote字符，请使用cluster模式。
 6. cluster如果读取csv时解析失败，将会把失败的列值设为NULL，继续导入流程，但local模式会直接报错，不会继续导入。
+7. csv的编码格式推荐使用UTF-8，不支持GB一类的中文字符编码。如果csv导入后表数据中的中文为乱码，请先转换csv源数据的格式再导入，参考命令：
+    ```bash
+    iconv -f GBK -t UTF-8 gbk.csv > utf8.csv
+    ```
 
 ## PutIfAbsent说明