Copy over default.nix from the rust-gpu repo, changing the name field to the name of this repo

Author: ky-bean

default.nix

@@ -0,0 +1,33 @@
+let
+  pkgs = import <nixpkgs> {};
+in
+  with pkgs;
+    stdenv.mkDerivation rec {
+      name = "rust-gpu-shadertoys";
+
+      # Workaround for https://github.com/NixOS/nixpkgs/issues/60919.
+      # NOTE(eddyb) needed only in debug mode (warnings about needing optimizations
+      # turn into errors due to `-Werror`, for at least `spirv-tools-sys`).
+      hardeningDisable = ["fortify"];
+
+      # Allow cargo to download crates (even inside `nix-shell --pure`).
+      SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
+
+      nativeBuildInputs = [rustup];
+
+      # Runtime dependencies (for the example runners).
+      LD_LIBRARY_PATH = with xorg;
+        lib.makeLibraryPath [
+          vulkan-loader
+
+          # NOTE(eddyb) winit really wants `libxkbcommon` on Wayland for some reason
+          # (see https://github.com/rust-windowing/winit/issues/1760 for more info).
+          wayland
+          libxkbcommon
+
+          libX11
+          libXcursor
+          libXi
+          libXrandr
+        ];
+    }