README: Added overview of C++ interfaces
README: Added overview of C++ interfaces

Signed-off-by: Henry Bruce <57ea958cad66de244404958c9a01f7a4ad51b29e@intel.com>
Signed-off-by: Abhishek Malik <876019366d13664ffb738df1a8654f7b38f787b3@intel.com>

kissbac/upm,kissbac/upm,Jon-ICS/upm,pylbert/upm,whbruce/upm,g-vidal/upm,kissbac/upm,jontrulson/upm,nitirohilla/upm,g-vidal/upm,whbruce/upm,nitirohilla/upm,kissbac/upm,Propanu/upm,malikabhi05/upm,stefan-andritoiu/upm,malikabhi05/upm,Propanu/upm,whbruce/upm,pylbert/upm,andreivasiliu2211/upm,g-vidal/upm,whbruce/upm,whbruce/upm,malikabhi05/upm,skiselev/upm,Jon-ICS/upm,Propanu/upm,stefan-andritoiu/upm,andreivasiliu2211/upm,g-vidal/upm,intel-iot-devkit/upm,sasmita/upm,intel-iot-devkit/upm,malikabhi05/upm,sasmita/upm,g-vidal/upm,nitirohilla/upm,andreivasiliu2211/upm,pylbert/upm,sasmita/upm,jontrulson/upm,andreivasiliu2211/upm,sasmita/upm,skiselev/upm,malikabhi05/upm,stefan-andritoiu/upm,jontrulson/upm,malikabhi05/upm,pylbert/upm,spitfire88/upm,pylbert/upm,pylbert/upm,stefan-andritoiu/upm,g-vidal/upm,Propanu/upm,spitfire88/upm,spitfire88/upm,spitfire88/upm,Jon-ICS/upm,intel-iot-devkit/upm,intel-iot-devkit/upm,kissbac/upm,intel-iot-devkit/upm,jontrulson/upm,nitirohilla/upm,skiselev/upm,Jon-ICS/upm,skiselev/upm,skiselev/upm,skiselev/upm,nitirohilla/upm,stefan-andritoiu/upm,sasmita/upm,Jon-ICS/upm,Propanu/upm,spitfire88/upm,jontrulson/upm,andreivasiliu2211/upm,stefan-andritoiu/upm,Propanu/upm,intel-iot-devkit/upm