doc: user-guide.md now lives at https://github.com/NixOS/nixpkgs/blob/master/doc/haskell-users-guide.md
doc: user-guide.md now lives at https://github.com/NixOS/nixpkgs/blob/master/doc/haskell-users-guide.md

Fuuzetsu/cabal2nix,bennofs/cabal2nix