Copy doc from 1.3.8 to dev

[zhongjiajie]

I copy our document from user_doc/1.3.8 to user_doc/dev. It add a place to show and keep our laster document, which mean user could check laster document in our website. What more, this change make contributor can change related document after their code merged to https://github.com/apache/dolphinscheduler.

When we want to release our new document to website, we just need to add new folder in docs/zh-cn and docs/en-us and copy content from folder dev, and then add file doc<version>.js and change site.js in folder site_config

[zhongjiajie]

I put original dev document into independently section named To be Classification. The screenshot as below:

[zhongjiajie]

PTAL @CalvinKirs @lenboo @dailidong

[zhongjiajie]

Closes it due to #453