Update README getting started instructions

[vkleen]

Closes #59

[GTrunSec]

Notice: Terraform has changed its license to the unfree software.

  Alternatively you can configure a predicate to allow specific packages:
         { nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
             "terraform"
           ];
         }

you can set the above config to the pkgs or make the pkgs.terraform.priovder to be an args.

[yannham]

@vkleen I don't know why it slipped under the radar of my notification, but I missed that PR. Would that make sense to include @GTrunSec 's suggestion about the Terraform License change?

[GTrunSec]

@vkleen @yannham Alternatively, we can use https://github.com/opentofu/opentofu as default. Also, I have added a git-backend for the tf-ncl with devshell https://github.com/GTrunSec/tf-ncl-workflow

[vkleen]

I think the allowUnfreePredicate suggestion is good. I've added it in the latest commits and update the nixpkgs flake input on the way. That was necessary anyways for the license change to show up. At some point, a few of the scripts here will need fixes for Nickel's new CLI but that will go in another PR.