chore: Add flake.nix

Author: lambdalisue

.envrc.sample

@@ -0,0 +1 @@
+use flake

flake.lock

@@ -0,0 +1,31 @@
+{
+  description = "Development environment for jsr-probitas/documents";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    probitas.url = "github:jsr-probitas/probitas";
+    probitas.inputs.nixpkgs.follows = "nixpkgs";
+    probitas.inputs.flake-utils.follows = "flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, probitas }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        probitasPkg = probitas.packages.${system}.probitas;
+      in {
+        packages.default = probitasPkg;
+
+        devShells.default = pkgs.mkShell {
+          packages = [
+            pkgs.deno
+            probitasPkg
+          ];
+
+          shellHook = ''
+            export DENO_NO_UPDATE_CHECK=1
+          '';
+        };
+      });
+}