new: add nix flake + instructions on how to use

.gitignore

@@ -204,3 +204,7 @@ sftp-config.json
 # Vagrant
 .vagrant/
 ubuntu-xenial-16.04-cloudimg-console.log
+
+
+# Direnv
+.direnv

README.md

@@ -14,9 +14,10 @@ completed.
 
 You have a few options for installation:
 
-- Install the dependencies for the koans (such as Clojure) on your machine
-- Use Vagrant and the configuration in this repository
-- Use Docker
+- Install the dependencies for the koans (such as Clojure) on your machine.
+- Use Vagrant and the configuration in this repository.
+- Use Docker.
+- Use Nix Develop environment.
 
 Instructions for each option are below!
 
@@ -69,6 +70,21 @@ To start up a REPL:
 docker run --rm -it -v $(pwd):/app -w /app clojure lein repl
 ```
 
+### Installation with Nix Develop Environment
+
+Make sure you have [nix](https://nixos.wiki/wiki/Nix_Installation_Guide) setup,
+then run: 
+
+```
+nix --experimental-features 'nix-command flakes' develop
+```
+
+This will drop you into a shell with all the required dependencies installed.
+To run koans, in the root of the repository run:
+
+```
+lein koan run
+```
 
 ## Running the Koans
 

flake.nix

@@ -0,0 +1,31 @@
+{
+  description = "Clojure Koans";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = inputs@{ self, nixpkgs, flake-utils, ... }:
+  flake-utils.lib.eachDefaultSystem (system:
+  let
+    overlays = [ ];
+
+    pkgs = import nixpkgs {inherit system overlays;};
+
+    additionalPkgs = with pkgs; [  ];
+
+    buildPkgs = with pkgs; [ clojure leiningen ]; 
+
+    project = pkgs.stdenv.mkDerivation {
+      name = "koans-env";
+      root = self;
+      buildInputs = buildPkgs;
+      shellInputs = additionalPkgs;
+    };
+
+  in {
+  defaultPackage = project;
+  devShell = project;
+  });
+}