Add Nix flake

flake.nix

@@ -0,0 +1,60 @@
+{
+  description = "Retrospace website development environment";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-22.11";
+    flake-utils.url = "github:numtide/flake-utils";
+    devshell = {
+      url = "github:numtide/devshell";
+      inputs = {
+        flake-utils.follows = "flake-utils";
+        nixpkgs.follows = "nixpkgs";
+      };
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, devshell }:
+    flake-utils.lib.eachDefaultSystem (system: {
+      devShell =
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+
+            overlays = [ devshell.overlays.default ];
+          };
+        in
+        pkgs.devshell.mkShell {
+          name = "Retrospace website development environment";
+          packages = with pkgs; [
+            (pkgs.ruby_3_1.withPackages
+              (ps: with ps; [
+                bundler
+                jekyll
+                kramdown-parser-gfm
+                webrick
+              ])
+            )
+            nixpkgs-fmt
+            isort
+          ];
+          env = [ ];
+          commands = [
+            {
+              name = "retrospace:lint";
+              category = "Maintenance";
+              help = "Lint all the files in project";
+              command = ''
+                nixpkgs-fmt *.nix
+              '';
+            }
+            {
+              name = "retrospace:deploy";
+              help = "Deploy the website";
+              command = ''
+                jekyll build && rsync -v -rz --checksum --delete ./_site/ endor:/var/www/retrospace.be
+              '';
+            }
+          ];
+        };
+    });
+}