configure editor.

add install directions to readme.

README.md

@@ -0,0 +1,8 @@
+# .plan: edit files
+
+## install
+
+```bash
+uv tool install --from https://git.publicmatt.com/public/plan.git plan
+```
+

src/plan/path.py

@@ -1,5 +1,7 @@
-from pathlib import Path
+import os
 from datetime import datetime
+from pathlib import Path
+
 from .templates import default
 
 
@@ -16,4 +18,5 @@ def open(plan: Path):
         plan.touch()
         with plan.open("rw") as f:
             f.write(default())
-    subprocess.run(["nvim", str(plan)])
+    editor = os.getenv("EDITOR", "nvim")
+    subprocess.run([editor, str(plan)])