New example for adding unspecified dependencies

[timhae]

Thanks for your great tool, it seems like the default structure has changed since the example for adding unspecified dependencies was created, how would it look like now? I would like to provide the buildInputs of buildPackage in composer-env.nix, ideally changing only files that are not generated, similar to #15 . I would like to provide glibcLocales to the package in this PR: https://github.com/NixOS/nixpkgs/pull/184362/files