make: add target flash

Makefile

@@ -225,6 +225,9 @@ ULIBS = -lm
 RULESPATH = $(CHIBIOS)/os/common/startup/ARMCMx/compilers/GCC
 include $(RULESPATH)/rules.mk
 
+flash: build/ch.bin
+	dfu-util -d 0483:df11 -a 0 -s 0x08000000:leave -D build/ch.bin
+
 TAGS: Makefile
 	@etags *.[ch] NANOVNA_STM32_F072/*.[ch] $(shell find ChibiOS/os/hal/ports/STM32/STM32F0xx ChibiOS/os -name \*.\[ch\] -print) 
 	@ls -l TAGS