Update README with build instructions

Author: Fabien-Chouteau

README.md

@@ -2,3 +2,22 @@
 A G-code parser and CNC controller (in Ada)
 
 For more info: http://blog.adacore.com/make-with-ada-arm-cortex-m-cnc-controller
+
+##  Build instructions
+
+### Gcode Viewer
+
+ - Download and install the [GNAT and GtkAda packages](http://libre.adacore.com/download/configurations) in the same directory
+ - Start GPS (GNAT Programing Studio)
+ - Open the project file gcode_viewer/gcode_viewer.gpr
+ - Use the "Build all" button to compile
+ - use the "Run Main: main_gtkada" button to start the application
+
+### CNC controller on the STM32F4 Discovery
+
+- Make sure to get all the Git submodules "$ git submodules update"
+- Download and install the [GNAT for ARM package](http://libre.adacore.com/download/configurations)
+- Start GPS (GNAT Programing Studio)
+- Open the project file stm32f4-disco_controller/stm32f4_disco_CNC_controller.gpr
+- Use the "Build all" button to compile
+- use the "Flash to board" button to program the STM32F4 Discovery board