feat(nix): user flake instead regular shell.nix

flake.nix

@@ -0,0 +1,24 @@
+{
+  description = "Nix flake for building latex document";
+
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+  };
+
+  outputs =
+    inputs@{
+      nixpkgs,
+      flake-parts,
+      systems,
+      ...
+    }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [ "x86_64-linux" ];
+      imports = [
+        inputs.treefmt-nix.flakeModule
+        ./nix/default.nix
+      ];
+    };
+}