Make this repo a fork of of bids-specification

[yarikoptic]

To simplify preparation of PRs for BIDS 2.0 , having it as a fork would establish logical relationship IMHO

Steps to take

• [x] Make default branch with README to be eg README and unique you this repo
• [ ] setup mirroring of master branch from bids-specification
• [ ] ask GitHub support to announce this to be a fork

[yarikoptic]

actually I think I would give up this idea for now -- I think it might just

• cause more confusion
• hide away work towards 2.0
• ...

so for now I will remove all pushed tags/branches