update logger README to include detailed usage instructions and examples

Signed-off-by: YoungSoo Shin <shinys000114@gmail.com>

example/logger/csv_2_plot.py

@@ -1,5 +1,4 @@
 import argparse
-
 import matplotlib.dates as mdates
 import matplotlib.pyplot as plt
 import pandas as pd

example/logger/logger.py

@@ -113,9 +113,9 @@ class OdroidPowerLogger:
                             ts_iso_csv = ts_dt.isoformat(timespec='milliseconds').replace('+00:00', 'Z')
                             row = [
                                 ts_iso_csv, sensor_data.uptime_ms,
-                                sensor_data.vin.voltage, sensor_data.vin.current, sensor_data.vin.power,
-                                sensor_data.main.voltage, sensor_data.main.current, sensor_data.main.power,
-                                sensor_data.usb.voltage, sensor_data.usb.current, sensor_data.usb.power
+                                f"{sensor_data.vin.voltage:.3f}", f"{sensor_data.vin.current:.3f}", f"{sensor_data.vin.power:.3f}",
+                                f"{sensor_data.main.voltage:.3f}", f"{sensor_data.main.current:.3f}", f"{sensor_data.main.power:.3f}",
+                                f"{sensor_data.usb.voltage:.3f}", f"{sensor_data.usb.current:.3f}", f"{sensor_data.usb.power:.3f}"
                             ]
                             csv_writer.writerow(row)