Add Nix flake

Overview: https://tonyfinn.com/blog/nix-from-first-principles-flake-edition/

.gitignore

@@ -3,3 +3,5 @@
 /tilesheets
 ftb.json
 *.exe
+# nix build generates this
+/result

flake.nix

@@ -0,0 +1,49 @@
+{
+  description =  "Stuff for FTB wiki";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+	systems.url = "github:nix-systems/default";
+    flake-utils.url = "github:numtide/flake-utils";
+	flake-utils.inputs.systems.follows = "systems";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+	rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
+	rust-overlay.inputs.flake-utils.follows = "flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, rust-overlay, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs { inherit system overlays; };
+        rustVersion = pkgs.rust-bin.stable.latest.default;
+      in {
+        devShell = pkgs.mkShell {
+          buildInputs = [ (rustVersion.override { extensions = [ "rust-src" ]; }) ];
+        };
+
+        packages = {
+          ftb-rs = pkgs.rustPlatform.buildRustPackage rec {
+            pname = "ftb-rs";
+            version = "0.1.0";
+            src = ./.;
+
+            cargoLock = {
+              lockFile = ./Cargo.lock;
+              outputHashes = {
+                "mediawiki-0.0.1" = "sha256-iekGJXWT4n5ad4nlu27sNfuydL9quvEe4Bw327LgaBE=";
+              };
+            };
+
+            buildInputs = [ ] ++ pkgs.lib.optional pkgs.stdenv.isDarwin [ pkgs.darwin.apple_sdk.frameworks.Foundation pkgs.darwin.apple_sdk.frameworks.Security ];
+          };
+        };
+
+        defaultPackage = self.packages.${system}.ftb-rs;
+
+        apps.default = {
+          type = "app";
+          program = "${self.packages.${system}.ftb-rs}/bin/ftb";
+        };
+      });
+}