We think we should split the usage and architecture because of clear organization and future extension (we may add more usage guide)

* migrate en doc from old dir

* fix typo

* fix typo

* fix typo

* add input_spec cn

* add input_spec cn

* fix === style

* fix file name typo

* add ref

* add en doc

* fix en doc

* refine according reviewer

* remove user comment

* refine doc

* refine doc

* add migration test=develop

* fix_logs test=develop

* fix_migration_guide and add dygraph to static test=develop

* fix_install test=develop

* fix install and args

* fix_style test=develop

* fix docs test=develop

As the title.

当前只是最基本的文档，我正在添加：

支持和不支持的语法情况
高级debug功能使用方法文档
本文档的架构也需要添加画图更加直观
对应英文文档