Better error handling instructions

Tools/px_uploader.py

@@ -459,6 +459,7 @@ if os.path.exists("/usr/sbin/ModemManager"):
 # Load the firmware file
 fw = firmware(args.firmware)
 print("Loaded firmware for %x,%x, waiting for the bootloader..." % (fw.property('board_id'), fw.property('board_revision')))
+print("If the board does not respond within 1-2 seconds, unplug and re-plug the USB connector.")
 
 # Spin waiting for a device to show up
 while True:
@@ -508,6 +509,7 @@ while True:
                 except Exception:
                         # most probably a timeout talking to the port, no bootloader, try to reboot the board
                         print("attempting reboot on %s..." % port)
+                        print("if the board does not respond, unplug and re-plug the USB connector.")
                         up.send_reboot()
                         # wait for the reboot, without we might run into Serial I/O Error 5 
                         time.sleep(0.5)