Add nix shell and use it in the envrc

.envrc

@@ -1 +1,2 @@
+use_nix
 layout poetry

shell.nix

@@ -0,0 +1,15 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+
+  buildInputs = [
+    pkgs.python3
+    pkgs.poetry
+    pkgs.xdotool
+  ];
+
+  # DOES NOT WORK. LD_LIBRARY_PATH="${pkgs.xdotool}/lib";
+  # (no longer needed since we don't use libxdo; just use xdotool)
+
+}
+