A Unix shell script matching the functionality flash_dfu.bat

(cherry picked from commit fd192ab28fde1dac204b19a6fd446728a3b35647)

firmware/flash_dfu.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+# This is a Linux/Unix script to do USB DFU (Device Firmware Update).
+#
+# The STM32 has multiple ways to write an application into the MCU.  One is
+# is USB DFU mode.
+# This can write a blank or overwrite a corrupted ECU, but does require
+# that the processor be set into DFU mode by holding down the 'Program' (AKA
+# 'Boot1') button at reset or power up.
+# Note: The 'Program' button is only checked immediately after reset.  The
+# button may be released after that instant.  A reset or power cycle may be
+# needed to exit DFU mode.
+#
+
+# Future: Consider if creating a build/rusefi.dfu install file is more
+# or less descriptive than multiple command line parameters.
+
+dfu-util --alt 0 --download build/rusefi.bin --dfuse-address 0x08000000 --reset
+
+# For Windows the batch file flash_dfu.bat runs the equivalent command
+#   DfuSeCommand.exe -c -d --fn build/rusefi.dfu