docs: Add documentation for building mraa with docker
docs: Add documentation for building mraa with docker

Signed-off-by: Nicolas Oliver <20d36bc264582663740c7fbd44ac057f4dd34220@intel.com>
Signed-off-by: Brendan Le Foll <3e0e8c4069934e8b47d99704927a85c66c0ceb33@intel.com>

alext-mkrs/mraa,Propanu/mraa,yongli3/mraa,ncrastanaren/mraa,arfoll/mraa,KurtE/mraa,KurtE/mraa,stefan-andritoiu/mraa,malikabhi05/mraa,stefan-andritoiu/mraa,g-vidal/mraa,ncrastanaren/mraa,sergev/mraa,intel-iot-devkit/mraa,malikabhi05/mraa,KurtE/mraa,Propanu/mraa,ncrastanaren/mraa,stefan-andritoiu/mraa,arfoll/mraa,arfoll/mraa,Propanu/mraa,malikabhi05/mraa,intel-iot-devkit/mraa,malikabhi05/mraa,sergev/mraa,intel-iot-devkit/mraa,intel-iot-devkit/mraa,yongli3/mraa,Propanu/mraa,g-vidal/mraa,ncrastanaren/mraa,yongli3/mraa,sergev/mraa,alext-mkrs/mraa,g-vidal/mraa,KurtE/mraa,sergev/mraa,alext-mkrs/mraa,malikabhi05/mraa,yongli3/mraa,alext-mkrs/mraa,arfoll/mraa,sergev/mraa,yongli3/mraa,intel-iot-devkit/mraa,stefan-andritoiu/mraa,g-vidal/mraa,arfoll/mraa,KurtE/mraa,g-vidal/mraa,Propanu/mraa,stefan-andritoiu/mraa,ncrastanaren/mraa,alext-mkrs/mraa