modify docstring, type hint

sohstationviewer/view/plotting/plotting_widget/plotting_widget_helper.py

-from typing import List, Optional
+from typing import Dict, Optional
 import numpy as np
 
 
 def get_index_from_data_picked(
-        chan_data: List[np.ndarray], tm: float, val: float) -> Optional[int]:
+        chan_data: Dict, tm: float, val: float) -> np.ndarray:
     """
     Get index of data picked
     :param chan_data: dict of data to plot that includes 'times', 'data' key
     :param tm: epoch time of a clicked point
     :param val: data value of a clicked point
-    :return section_idx: index of tm inside np.ndarray found
+    :return real_indexes: list index of data point inside np.ndarray found
     """
     if chan_data['chan_db_info']['plotType'] == 'upDownDots':
         # actual plotting has value -0.5 or 0.5;