Proposal: reorganisation of documents

[PsiACE]

Background

At #2753, we have a proposal for moving the docs directory.

Purposes

• Easier to find documentation for newcomers
• Convenient collection of RFCs

Plan

• Move the developer documentation to the docs directory. (rfcs / contributing)
• Remove the databend directory. (I don't think we will have many websites or maintain a complex node project in this repo)

- docs
  - rfcs
  - contributing
- website
  - src
  - docs
    - dev -> link to /docs
    - user
    - overview

Credits

@Xuanwo Plan for this reorganisation

[BohuTANG]

How about link - docs to website/src/docs/dev?