Todo: Missing features

[Thesola10]

These are features that I intend to add to Nixie, but haven't gotten around to yet.

Some of these features' description may not cover all the information needed to implement them, but that is not a mistake.

• .gitignore and .gitattributes should be set up
• Implement project templates
• --nixie-* command line options
• Choose nix or nix-shell filename depending on other .nix files
• Check if local nixpkgs/nixos channel is more recent on update