Adding a README for the nRF5 port

nrf5/README.md

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+# MicroPython port to the NRF5
+
+This is a port of MicroPython to the Nordic nRF5 series of chips. 
+
+## Supported features
+
+* UART
+* SPI
+* LEDs
+* Pins
+* ADC
+* I2C
+* PWM (nRF52 only)
+* Temperature
+* RTC
+* Some BLE support including _REPL over BLE_
+
+Note that this port is still a work-in-progress and some modules are not fully feature complete.
+
+## Tested hardware
+* nRF51
+* nRF52
+  * [PCA10040](http://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.nrf52%2Fdita%2Fnrf52%2Fdevelopment%2Fnrf52_dev_kit.html) 
+  * [D52Q](https://www.dynastream.com/components/d52)
+  * [Adafruit Feather nRF52](https://www.adafruit.com/product/3406)
+
+## Build steps
+
+Example is for the Adafruit Feather nRF52:
+
+```
+> sudo apt-get install build-essential libffi-dev pkg-config gcc-arm-none-eabi git python python-pip
+> git clone https://github.com/adafruit/Adafruit_nRF52_Arduino.git
+> cd Adafruit_nRF52_Arduino/tools/nrfutil-0.5.2/
+> sudo pip install -r requirements.txt
+> sudo python setup.py install
+> cd ../../..
+> git clone https://github.com/tralamazza/micropython.git nrf5_no_sdk
+> cd nrf5_no_sdk/
+> git submodule update --init
+> make -C mpy-cross
+> cd nrf5/
+> make BOARD=feather52
+> make BOARD=feather52 dfu-gen
+> make BOARD=feather52 dfu-flash
+```