chore(nix): Add nix flake for spices (#39)

Author: metame

.gitignore

@@ -1,3 +1,8 @@
 _build
 _opam
 .DS_Store
+
+# nix ignores
+.direnv
+result
+.envrc

flake.lock

@@ -0,0 +1,41 @@
+{
+  description = "A little TUI framework for OCaml";
+
+  inputs.colors.url = "github:ocaml-tui/colors";
+  inputs.tty.url = "github:ocaml-tui/tty";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [ "x86_64-linux" "aarch64-linux" "aarch64-darwin" "x86_64-darwin" ];
+      perSystem = { config, self', inputs', pkgs, system, ... }:
+        let
+          inherit (pkgs) ocamlPackages mkShell;
+          inherit (ocamlPackages) buildDunePackage;
+          version = "0.0.2";
+        in
+          {
+            devShells = {
+              default = mkShell {
+                buildInputs = [ ocamlPackages.utop ];
+                inputsFrom = [ self'.packages.spices ];
+              };
+            };
+
+            packages = {
+              spices = buildDunePackage {
+                inherit version;
+                pname = "spices";
+                propagatedBuildInputs = with ocamlPackages; [
+                  inputs'.colors.packages.default
+                  inputs'.tty.packages.default
+                  (mdx.override {
+                    inherit logs;
+                  })
+                ];
+                src = ./.;
+              };
+            };
+          };
+    };
+}