Update flake for COSMIC itself

flakes/COSMIC/flake.nix

@@ -0,0 +1,44 @@
+{
+  description = "COSMIC Development Environment";
+
+  inputs = {
+    nixpkgs = {url = "github:NixOS/nixpkgs/nixpkgs-unstable";};
+    flake-utils = {url = "github:numtide/flake-utils";};
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      inherit (nixpkgs.lib) optional;
+      pkgs = import nixpkgs {inherit system;};
+      fhs = pkgs.buildFHSUserEnv {
+        name = "COSMIC";
+        targetPkgs = pkgs: (with pkgs; [
+          # There is a lot here, because I am not sure about your system. :)
+          xorg.libX11 
+          xorg.libXext 
+          xorg.libxcb 
+          udev
+        #runScript = "bash -c ./pico8";
+      };
+    in {
+      devShell = pkgs.mkShell {
+        buildInputs = with pkgs; [
+          fhs
+        ];
+        shellHook = ''
+          if [ -e pico8 ]
+          then
+              tput setaf 2; echo "Pico-8 binary present. Type 'pico8' to get started."; tput sgr0;
+          else
+              tput setaf 3; echo "No Pico-8 binary present. Please download it."; tput sgr0;
+              echo "You can purchase it here:"
+              tput setaf 2; echo "https://www.lexaloffle.com/pico-8.php"; tput sgr0;
+          fi
+        '';
+      };
+    });
+}