firmata.md: Add basic firmata docs
firmata.md: Add basic firmata docs

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

ncrastanaren/mraa,KurtE/mraa,arunlee77/mraa,petreeftime/mraa,andreivasiliu2211/mraa,Pillar1989/mraa,stefan-andritoiu/mraa,jontrulson/mraa,ProfFan/mraa,sergev/mraa,ProfFan/mraa,malikabhi05/mraa,stefan-andritoiu/mraa,jontrulson/mraa,w4ilun/mraa,stefan-andritoiu/mraa-gpio-chardev,stefan-andritoiu/mraa,Hbrinj/mraa,intel-iot-devkit/mraa,stefan-andritoiu/mraa-gpio-chardev,yongli3/mraa,Pillar1989/mraa,Hbrinj/mraa,whbruce/mraa,stefan-andritoiu/mraa-gpio-chardev,alext-mkrs/mraa,spitfire88/mraa,alext-mkrs/mraa,arunlee77/mraa,w4ilun/mraa,ncrastanaren/mraa,Propanu/mraa,sergev/mraa,jontrulson/mraa,g-vidal/mraa,whbruce/mraa,ncrastanaren/mraa,yongli3/mraa,w4ilun/mraa,g-vidal/mraa,ProfFan/mraa,g-vidal/mraa,stefan-andritoiu/mraa,yongli3/mraa,andreivasiliu2211/mraa,KurtE/mraa,arfoll/mraa,KurtE/mraa,w4ilun/mraa,intel-iot-devkit/mraa,ProfFan/mraa,KurtE/mraa,g-vidal/mraa,Propanu/mraa,whbruce/mraa,ncrastanaren/mraa,malikabhi05/mraa,jontrulson/mraa,alext-mkrs/mraa,jontrulson/mraa,Propanu/mraa,sergev/mraa,stefan-andritoiu/mraa-gpio-chardev,sergev/mraa,Jon-ICS/mraa,arunlee77/mraa,sergev/mraa,intel-iot-devkit/mraa,Propanu/mraa,stefan-andritoiu/mraa-gpio-chardev,Pillar1989/mraa,intel-iot-devkit/mraa,whbruce/mraa,arfoll/mraa,Jon-ICS/mraa,arfoll/mraa,Jon-ICS/mraa,yongli3/mraa,malikabhi05/mraa,petreeftime/mraa,arfoll/mraa,Hbrinj/mraa,arunlee77/mraa,arfoll/mraa,andreivasiliu2211/mraa,intel-iot-devkit/mraa,alext-mkrs/mraa,malikabhi05/mraa,petreeftime/mraa,Propanu/mraa,yongli3/mraa,spitfire88/mraa,petreeftime/mraa,g-vidal/mraa,stefan-andritoiu/mraa,alext-mkrs/mraa,spitfire88/mraa,malikabhi05/mraa,andreivasiliu2211/mraa,ncrastanaren/mraa,spitfire88/mraa,KurtE/mraa,Hbrinj/mraa