Create docs folder

[sorki]

• [x] 01-Prelude.org
• [x] 02-Hacking.org
  • [x] mention Cachix cache
  • [x] nix-build matrix.nix
  • [x] nix-build --argstr compiler ghc963
  • [x] updating CI
  • [x] ghcid
  • [ ] hie

[sorki]

hie section is omitted as I don't use it at the moment but considering reviving my old setup. @squalus feel free to add it if you want.