Add image showing which pads to bridge for DFU

README.md

 
 Set the Boot switch (SW1) on the PD Buddy Sink to the position not marked on
 the silkscreen to set the device to DFU mode.  If your Sink doesn't have a Boot
-switch, you can simply bridge the two long, close-together pads on the
-footprint for SW1 with a blob of solder to achieve the same effect.  Once the
+switch installed, you can simply bridge the two pads of SW1 circled in [this
+image][dfu pads] with a blob of solder to achieve the same effect.  Once the
 Sink is set to DFU mode, plug it into your computer.  Flash the firmware with:
 
     $ dfu-util -a 0 -s 0x08000000:leave -D build/pd-buddy-firmware.bin
 Don't forget to set the switch back to normal mode (or remove the solder blob)
 after unplugging the device.
 
+[dfu pads]: docs/dfu_pads.jpg
+
 ### stlink
 
 If you have an ST-LINK/V2, you can use it to flash the firmware via SWD as