docs/building.md: add note about forcing a static build of mraa
docs/building.md: add note about forcing a static build of mraa

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

whbruce/mraa,stefan-andritoiu/mraa,ncrastanaren/mraa,arfoll/mraa,w4ilun/mraa,KurtE/mraa,malikabhi05/mraa,intel-iot-devkit/mraa,arunlee77/mraa,arunlee77/mraa,stefan-andritoiu/mraa-gpio-chardev,Jon-ICS/mraa,arfoll/mraa,KurtE/mraa,ncrastanaren/mraa,malikabhi05/mraa,arunlee77/mraa,yongli3/mraa,jontrulson/mraa,malikabhi05/mraa,yongli3/mraa,alext-mkrs/mraa,whbruce/mraa,spitfire88/mraa,intel-iot-devkit/mraa,Propanu/mraa,alext-mkrs/mraa,sergev/mraa,stefan-andritoiu/mraa-gpio-chardev,intel-iot-devkit/mraa,alext-mkrs/mraa,arfoll/mraa,yongli3/mraa,Propanu/mraa,stefan-andritoiu/mraa-gpio-chardev,yongli3/mraa,jontrulson/mraa,stefan-andritoiu/mraa,malikabhi05/mraa,Jon-ICS/mraa,stefan-andritoiu/mraa-gpio-chardev,stefan-andritoiu/mraa,Propanu/mraa,intel-iot-devkit/mraa,jontrulson/mraa,w4ilun/mraa,sergev/mraa,spitfire88/mraa,g-vidal/mraa,jontrulson/mraa,w4ilun/mraa,stefan-andritoiu/mraa-gpio-chardev,malikabhi05/mraa,sergev/mraa,yongli3/mraa,Propanu/mraa,ncrastanaren/mraa,intel-iot-devkit/mraa,g-vidal/mraa,spitfire88/mraa,KurtE/mraa,jontrulson/mraa,sergev/mraa,whbruce/mraa,stefan-andritoiu/mraa,alext-mkrs/mraa,alext-mkrs/mraa,w4ilun/mraa,Jon-ICS/mraa,stefan-andritoiu/mraa,g-vidal/mraa,whbruce/mraa,ncrastanaren/mraa,arfoll/mraa,Propanu/mraa,arunlee77/mraa,g-vidal/mraa,spitfire88/mraa,sergev/mraa,KurtE/mraa,ncrastanaren/mraa,g-vidal/mraa,KurtE/mraa,arfoll/mraa