Add nix/flake files

.envrc

@@ -0,0 +1,2 @@
+use flake
+watch_file shell.nix

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1659877975,
+        "narHash": "sha256-zllb8aq3YO3h8B/U0/J1WBgAL8EX5yWf5pMj3G0NAmc=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "c0e246b9b83f637f4681389ecabcb2681b4f3af0",
+        "type": "github"
+      },
+      "original": {
+        "id": "flake-utils",
+        "type": "indirect"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1663491030,
+        "narHash": "sha256-MVsfBhE9US5DvLtBAaTRjwYdv1tLO8xjahM8qLXTgTo=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "767542707d394ff15ac1981e903e005ba69528b5",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "Project Kyoku";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem
+      (system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+        in
+        {
+          devShell = import ./shell.nix { inherit pkgs; };
+        }
+      );
+}

shell.nix

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+{
+  pkgs     ? import <nixpkgs> {},
+  unstable ? import <nixos-unstable> {},
+}:
+
+with pkgs;
+mkShell {
+  buildInputs = [ sfml ];
+  nativeBuildInputs = [ ccls cmake ];
+}