[DEVOPS-1083] nix: Reference documentation from top of default.nix
[DEVOPS-1083] nix: Reference documentation from top of default.nix

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype