LOAD DATA 文档描述补充参数说明和常见问题

[imtbkcat]

Feature Request

This repository is ONLY used to solve problems related to DOCS-CN.
For other issues (TiDB, TiKV, etc), please move to other repositories.

1. Did you encounter a certain issue about the documentation? If yes, please describe the issue that relates to your feature request.

LOAD DATA 文档 中对于 LOAD DATA 各个参数没有具体的说明，也没有操作数据源的说明。

2. Please describe your suggestion or addition.

• 补充参数说明
• 给出一个连贯可操作的例子
• 对于常见问题给出链接

3. If convenient, please provide reference materials (Blog, Stack Overflow, etc).

[anotherrachel]

I have assigned this issue to you. I'll close this when you open the pull request. Thank you for refining this doc!