Describe how to create fork in README

.envrc

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

README.md

@@ -16,6 +16,11 @@ fix it.
 git clone --recursive git@git.wip.sh:<your-username>/lua-exercises.git
 ```
 
+Once you have a local clone of the repo, `cd` into the directory and
+run `nix develop .` to activate the development environment.  The
+first time you do this it might take a little while but it should be
+fairly fast afterwards.
+
 ## Doing the Exercises
 
 It's recommended that you roughly stick to the defined order of the

flake.lock

@@ -0,0 +1,40 @@
+{
+  "nodes": {
+    "flake-schemas": {
+      "locked": {
+        "lastModified": 1697467827,
+        "narHash": "sha256-j8SR19V1SRysyJwpOBF4TLuAvAjF5t+gMiboN4gYQDU=",
+        "rev": "764932025c817d4e500a8d2a4d8c565563923d29",
+        "revCount": 29,
+        "type": "tarball",
+        "url": "https://api.flakehub.com/f/pinned/DeterminateSystems/flake-schemas/0.1.2/018b3da8-4cc3-7fbb-8ff7-1588413c53e2/source.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://flakehub.com/f/DeterminateSystems/flake-schemas/%2A.tar.gz"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1702346276,
+        "narHash": "sha256-eAQgwIWApFQ40ipeOjVSoK4TEHVd6nbSd9fApiHIw5A=",
+        "rev": "cf28ee258fd5f9a52de6b9865cdb93a1f96d09b7",
+        "revCount": 553141,
+        "type": "tarball",
+        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.2311.553141%2Brev-cf28ee258fd5f9a52de6b9865cdb93a1f96d09b7/018c652c-2ff2-777b-bade-dae9c2abe1e1/source.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://flakehub.com/f/NixOS/nixpkgs/%2A.tar.gz"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-schemas": "flake-schemas",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "Environment for Lua programming exercises";
+  inputs = {
+    flake-schemas.url = "https://flakehub.com/f/DeterminateSystems/flake-schemas/*.tar.gz";
+    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/*.tar.gz";
+  };
+
+  outputs = { self, flake-schemas, nixpkgs }:
+    let
+      supportedSystems = [
+        "x86_64-linux"
+        "aarch64-darwin"
+        "x86_64-darwin"
+        "aarch64-linux"
+      ];
+      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+        pkgs = import nixpkgs { inherit system; };
+      });
+    in {
+      schemas = flake-schemas.schemas;
+      devShells = forEachSupportedSystem ({ pkgs }: {
+        default = pkgs.mkShell {
+          name = "lua-exercises";
+          packages = with pkgs; [ git lua ];
+        };
+      });
+    };
+}