add example .env file

.env.example

+# Environment variables go here, can be read by `python-dotenv` package:
+#
+#   `src/script.py`
+#   ----------------------------------------------------------------
+#    import dotenv
+#
+#    project_dir = os.path.join(os.path.dirname(__file__), os.pardir)
+#    dotenv_path = os.path.join(project_dir, '.env')
+#    dotenv.load_dotenv(dotenv_path)
+#   ----------------------------------------------------------------
+
+project_dir = "."
\ No newline at end of file