Add update script for a new vendor directory

Where we'll put pyproject.nix

vendor/update.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+import subprocess
+import shutil
+import json
+import os
+
+
+if __name__ == "__main__":
+    store_path = json.loads(
+        subprocess.check_output(
+            [
+                "nix-instantiate",
+                "--eval",
+                "--json",
+                "--expr",
+                'builtins.fetchGit { url = "git@github.com:adisbladis/pyproject.nix.git"; }',
+            ]
+        )
+    )
+
+    try:
+        shutil.rmtree("pyproject.nix")
+    except FileNotFoundError:
+        pass
+
+    os.mkdir("pyproject.nix")
+
+    for filename in os.listdir(f"{store_path}/lib"):
+        if filename.startswith("test") or not filename.endswith(".nix"):
+            continue
+        shutil.copy(f"{store_path}/lib/{filename}", f"pyproject.nix/{filename}")