add explanation in UI

dp_wizard/app/__init__.py

@@ -28,15 +28,10 @@ def ctrl_c_reminder():  # pragma: no cover
 
 def make_server_from_cli_info(cli_info: CLIInfo):
     def server(input: Inputs, output: Outputs, session: Session):  # pragma: no cover
-        cli_public_csv_path = cli_info.public_csv_path
         public_csv_path = reactive.value(  # noqa: F841 # TODO
-            "" if cli_public_csv_path is None else cli_public_csv_path
-        )
-
-        cli_private_csv_path = cli_info.public_csv_path
-        private_csv_path = reactive.value(
-            "" if cli_private_csv_path is None else cli_private_csv_path
+            cli_info.public_csv_path or ""
         )
+        private_csv_path = reactive.value(cli_info.private_csv_path or "")
 
         contributions = reactive.value(cli_info.contributions)
 

dp_wizard/app/dataset_panel.py

@@ -17,11 +17,33 @@ def dataset_ui():
 
     return ui.nav_panel(
         "Select Dataset",
+        ui.markdown(
+            """
+Choose **Public CSV** if you have a public data set, and are curious how
+DP can be applied: The preview visualizations will use your public data.
+
+Choose **Private CSV** if you only have a private data set, and want to
+make a release from it: The preview visualizations will only use
+simulated data, and apart from the headers, the private CSV is not
+read until the release.
+
+Choose both **Public CSV** and **Private CSV** if you have two files
+with the same structure. Perhaps the public CSV is older and no longer
+sensitive. Preview visualizations will be made with the public data,
+but the release will be made with private data.
+"""
+        ),
         # Doesn't seem to be possible to preset the actual value,
         # but the placeholder string is a good substitute.
         ui.input_file(
-            "csv_path",
-            ["Choose CSV file", ui.output_ui("choose_csv_demo_tooltip_ui")],
+            "public_csv_path",
+            ["Choose public CSV file", ui.output_ui("choose_csv_demo_tooltip_ui")],
+            accept=[".csv"],
+            placeholder=csv_placeholder,
+        ),
+        ui.input_file(
+            "private_csv_path",
+            "Choose private CSV file",
             accept=[".csv"],
             placeholder=csv_placeholder,
         ),