Update README.md

README.md

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 # flash_cc2531
 flash CC2531 USB dongle from your Raspberry, without Arduino nor CC Debugger.
+
+## prerequisites
+A Raspberry Pi 3 with raspbian and [wiringPi](http://wiringpi.com/) installed.
+
+## Getting Started
+
+Download and unpack the archive on your raspberry.
+Connect the following pins of the debug port to the GPIO port :
+pin 1 (GND)	-->	pin 39 (GND)
+pin 7 (reset)	-->	pin 35 (GPIO24)
+pin 3 (DC)	-->	pin 35 (GPIO27)
+pin 4 (DD)	-->	pin 35 (GPIO28)
+
+and insert the usb dongle in a port.
+
+test by running :
+```bash
+./cc_chipid
+```
+it should returns :
+```
+  ID = b524.
+```
+If you see 0000 or ffff, something is wrong and you should probably check your wiring.
+
+## Usage
+To save the content of the flash to save.hex file :
+```bash
+./cc_read save.hex
+```
+(takes around 2 minutes).
+
+To erase the flash :
+```bash
+./cc_erase
+```
+
+To flash file to cc2531 :
+```bash
+./cc_write CC2531ZNP-Pro.hex
+```
+(takes around 3 minutes).
+
+
+## License
+
+This project is licensed under the GPL v3 license (see COPYING).
+