Added a Makefile rule to flash with OpenOCD

Makefile

@@ -211,3 +211,8 @@ ULIBS =
 
 RULESPATH = $(CHIBIOS)/os/common/ports/ARMCMx/compilers/GCC
 include $(RULESPATH)/rules.mk
+
+# Special rules follow
+
+flash-openocd-stlink: $(BUILDDIR)/$(PROJECT).elf
+	openocd -f interface/stlink-v2.cfg -c "transport select hla_swd" -f target/stm32f0x.cfg -c "program $(BUILDDIR)/$(PROJECT).elf verify reset exit"

README.md

@@ -86,9 +86,10 @@ follows:
 
 ### OpenOCD
 
-OpenOCD can also be used to flash the firmware.  For example:
+OpenOCD can also be used to flash the firmware.  If your debug probe is an
+ST-LINK/V2, you can easily do this as follows:
 
-    $ openocd -f interface/stlink-v2.cfg -f target/stm32f0x.cfg -c "program build/pd-buddy-firmware.elf verify reset exit"
+    $ make flash-openocd-stlink
 
 ## Usage