I forgot to add the user manual. Just added it. You can check it out
https://github.com/sudar/RTuinOS/blob/master/doc/manual/RTuinOS-1.0-UserGuide.pdf
To answer your specific question.
Run this command first
export ARDUINO_HOME="your/path/to/arduino/installation/dir"
or you can set it in your `~/.bashrc`
Check-out/download the code and then from the root directory run the following command
make
This will show the list of targets available and also full documentation about how you can compile new applications or sample examples.
Try it out and let me know if you face any issues.
PS: I guess, I should update the Readme file with this information as well.