docs: Added NixOS prerequisites

[JanotLeLapin]

I added a minimal flake.nix sample that provides a dev shell with all required packages. This might be a lot when compared to other distributions prerequisites, but I figured I'd contribute anyways since I'm running NixOS right now and I can cargo tauri dev and cargo tauri build using this flake.

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[FabianLars]

Hi, thanks for contributing! Merging this may take a while because we are a bit unsure about nix and nixos right now, see https://github.com/tauri-apps/tauri/issues/8588#issuecomment-1891897399.

Also, this looks quite different to the 2 templates other people contributed to the stable docs: https://github.com/tauri-apps/tauri/issues/8588#issuecomment-1891897399 and to what i've seen in tauri's github issues. I'm not saying yours is wrong, but since i don't use nix/nixos myself i'd like to hear more nix users chime in :)

Lastly, is it possible to use stable rust? I'd really rather not recommend nightly in our docs.

[ninelore]

Aside from these issues LGTM