util: add shell.nix

shell.nix

@@ -0,0 +1,23 @@
+{ pkgs ? import <nixpkgs> {} }: let
+  pypkgs = pkgs.python3Packages;
+in pkgs.mkShell {
+  name = "kolibrios.org";
+
+  buildInputs = with pypkgs; [
+    python
+    virtualenv
+    pkgs.nodePackages.sass
+  ];
+
+  shellHook = ''
+    if [ ! -d "venv" ]; then
+      python -m venv .venv
+    fi
+
+    source .venv/bin/activate
+
+    if [ -f "requirements.txt" ]; then
+      pip install -r requirements.txt
+    fi
+  '';
+}