Update firmware_update.md

Author: nseidle

docs/firmware_update.md

@@ -108,6 +108,8 @@ esptool.exe --chip esp32 --port COM6 --baud 921600 --before default_reset --afte
 
 Where *COM6* is replaced with the COM port that the RTK product enumerated at and *RTK_Surveyor_Firmware_vxx.bin* is the firmware you would like to load.
 
+**Note:** Some users have reported the 921600bps baud rate does not work. Decrease this to 115200 as needed.
+
 Upon completion, your RTK device will reset and power down.
 
 ### macOS / Linux
@@ -120,6 +122,8 @@ py esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 921600 --before default_re
 
 Where */dev/ttyUSB0* is replaced with the port that the RTK product enumerated at and *RTK_Surveyor_Firmware_vxx.bin* is the firmware you would like to load.
 
+**Note:** Some users have reported the 921600bps baud rate does not work. Decrease this to 115200 as needed.
+
 Upon completion, your RTK device will reset and power down.
 
 ## Updating 4MB Surveyors