Add swagger api document

[narrowizard]

Description

We should add document for restful api.

Describe the solution you'd like

Recomended to use swagger with a lot great features and extensions, for example:

• generator documents from code with swaggo
• auto resolve apis with gin-swagger
• an easy-use web UI
  
• try out apis from web UI
  

[narrowizard]

/cc @joncodo @hezyin @klesh

[xgdyp]

I'll pick it！

[xgdyp]

I noticed the PR before was closed. Should I use go-swagger or just write down the docs?