updated docstring

dfm_tools/download.py

@@ -397,10 +397,13 @@ def copernicusmarine_credentials():
 
 def copernicusmarine_dataset_timeshift(ds, dataset_id):
     """
-    correct daily means from start-of-interval to center-of-interval times
+    correct daily means from start-of-interval to center-of-interval times.
+    Only the daily data is currently corrected with an offset of 12 hours.
+    This does not shift yearly, monthly, hourly, 3hourly or 6hourly data.
+    https://help.marine.copernicus.eu/en/articles/6820094-how-is-defined-the-nomenclature-of-copernicus-marine-data
     """
     if "P1D-m" in dataset_id:
-        # first check if dataset times are indeed at midnight (start-of-interval)
+        # check if dataset times are indeed at midnight (start-of-interval)
         assert (ds["time"].to_pandas().dt.hour == 0).all()
         # add offset to move to noon (center-of-interval)
         time_offset = pd.Timedelta(hours=12)