Update linux dependency documentation for NixOS (and nix)

[to-bak]

Objective

• Updates the linux-dependencies docs to 1) fix problems with nix alsa-lib, and 2) include additional documentation to run bevy with nix on non NixOS systems. (nix is a package manager that can be run outside of NixOS).

Solution

1. the nix alsa-lib package doesn't include alsa-plugins, which bevy depends on. Instead, use the alsa-lib-with-plugins package, which wraps alsa-plugins into alsa-lib. For more information see: alsa-lib: provide wrapper for run-time access to plugins NixOS/nixpkgs#277180
2. using nix on non NixOS systems, software like nixGL is required to correctly link graphics drivers.

Testing

• Tested on ubuntu 22.04 with nix.

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[mockersf]

nixGL seems to be a wrapper for OpenGL, but also contains nixVulkan which wraps Vulkan. Could you mention it first instead of running with nixGL?

[NthTensor]

Can't speak to the change, as I'm on NixOS and these instructions are for using the nix package manager on other operating systems. But seems to be correct.

[to-bak]

nixGL seems to be a wrapper for OpenGL, but also contains nixVulkan which wraps Vulkan. Could you mention it first instead of running with nixGL?

I updated the documentation to make this more clear. Please have another look