git: ignore nix env folders

[Pablito2020]

While working on another pull request, I found it frustrating that Git was tracking the .direnv and result/ folders (where Nix saves the program's closure).

This pull request adds these folders to the .gitignore to prevent them from being tracked.

[maximbaz]

Thanks for the PR! While I'm also using Nix, I think it's a bit opportunistic for us to expect that every single project in the world should git-ignore all particulates of every single operating system and environment 🙃 Have you considered putting those in your own global .gitignore file?

[Pablito2020]

Thank you for pointing that out! I initially thought the change might have been unintentional because the last commit that touches "code", c07ff23, added the flake.nix file.
So, given this was the last commit. I assumed this might have been overlooked.

From my perspective, I view Nix primarily as a build tool. When a repository includes support for tools like Nix and Direnv, I believe it should also account for ignoring the "artifact" files generated by these tools.
For example, with npm, it's standard to ignore the node_modules directory because it contains dependencies specific to the project. Similarly, Nix stores the results of building derivations in the result symlink, which I think should also be ignored to keep the repository clean.

This was the reasoning behind my PR. That said, I understand that Nix isn't yet a widely adopted tool, so its usage and related conventions might be unfamiliar to some. If you feel this change isn't necessary, I’m happy to close the PR—I just wanted to share the thought process behind it. 😊

[maximbaz]

I like this reasoning, thanks for sharing 😁