Update README.md

README.md

+This is a fork from **http://tmrh20.github.io/RF24** which can be build as a static library for Atmel Studio 7.
 
-**See http://tmrh20.github.io/RF24 for all documentation**
\ No newline at end of file
+Not all files are needed.
+
+Just copy the following structure into a GCC Static Library project in AS7:
+```
+utility\
+  ATXMega256D3\
+    compatibility.c
+    compatibility.h
+    gpio.cpp
+    gpio.h
+    gpio_helper.c
+    gpio_helper.h
+    includes.h
+    RF24_arch_config.h
+    spi.cpp
+    spi.h
+nRF24L01.h
+printf.h
+RF24.cpp
+RF24.h
+RF24_config.h
+```
+
+Only ATXMega256D3 is supported right now!
+
+** For further information please see http://tmrh20.github.io/RF24 for all documentation**