During setup, I wondered what the format of this variables is. While
searching for sample values, I noticed that people use these
inconsistently. So better be explicit.
I removed the paragraph from the README.md to avoid duplication.
The `ci.nix` file contains a number of improvements over
`buildable.nix`. For example, it
- honors `recurseForDerivations` to also build packages inside
attributes,
- builds all package outputs, and
- separates buildable and cacheable outputs such that packages having
`preferLocalBuild` are not cached.
Sadly nixpkgs haskell set is not stable and there's little
I can do to improve that, so official way to install cachix is via
known nixpkgs commit as above
