chore: add nix flake

flake.nix

@@ -0,0 +1,19 @@
+{
+  description = "Icons for the COSMIC desktop environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs = { self, nixpkgs }: {
+    packages.x86_64-linux.default =
+      with import nixpkgs { system = "x86_64-linux"; };
+      stdenv.mkDerivation {
+        nativeBuildInputs = [ just ];
+        name = "cosmic-icons";
+        src = self;
+        installPhase = "just prefix=$out install";
+      };
+
+  };  
+}