Update help documents

Update the following help documents:

• 04 _ Search List of Directories.help.md: Add instruction on limiting the time period to plot
• 40 _ Firmware Notice.help.md: Update list of channels affected by the old Pegasus firmware versions problem and add instruction on how to fix the problem

sohstationviewer/documentation/40 _ Firmware Notice.help.md

-Pegasus firmware was updated to record VEI in millivolts. 
-Previous versions of the firmware recorded VEI in microvolts.
+# Firmware notices
 
-We decided to apply VEI's conversion factor in newer version of Pegasus. 
-If user observe values higher than expected values for Pegasus, the data is of the older version.
\ No newline at end of file
+---------------------------
+---------------------------
+
+## Old Pegasus firmwares
+
+Some old Pegasus firmwares record a number of SOH channels in different units. 
+These channels included:
++ VEI: microvolts in old firmware, millivolts in new firmware
++ VDT: microdegrees C in old firmware, centidegrees C in new firmware
++ VM1-6: microvolts in old firmware, millivolts in new firmware
+
+Currently, SOHViewer only supports new versions of the Pegasus firmware. If the 
+plotted values of the channels listed above are higher than expected, the data 
+is recorded using old firmwares. This problem can be fixed by editing the 
+affected channels' conversion factor to reflect the old units (refer to the 
+View-Edit Database Tables section).