[Nix] A handful of missing features

[chris-martin]

Here's my to-do list for Nix (things I didn't include because I didn't know about them when I first wrote the tutorial):

• You can use interpolation inside a dotted expression, e.g. nixpkgs.pkgs.haskell.packages.${compiler}.callPackage
• Inherit, e.g. inherit a b; and inherit (foo) a b;
• You can use inherit in let binding context as well as in sets
• @-patterns similar to Haskell pattern matching. For example, in a function definition: f = args @ {x, y, z}: ...;
• or can be used to provide a default value when pulling a value out of a set, e.g. x.y or "defaultY"

[divayprakash]

@chris-martin Feel free to send a PR for the same!