build: add nix flake for rst2pdf

flake.lock

@@ -0,0 +1,43 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1667395993,
+        "narHash": "sha256-nuEHfE/LcWyuSWnS8t12N1wc105Qtau+/OdUAjtQ0rA=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "5aed5285a952e0b949eb3ba02c12fa4fcfef535f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1673455360,
+        "narHash": "sha256-oUR5O9QlBt1AnxDfXrHQZTpuOrYbRY8F+WZTpx02FA0=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a33466f87ece61963b6d71c2fa1c8c51f35f23ad",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "master",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,20 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/master";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShell = with pkgs; pkgs.mkShell {
+          buildInputs = [
+            just
+            python310Packages.rst2pdf
+          ];
+        };
+      });
+}