Add timer callback example.
Add timer callback example.

kwagyeman/openmv,kwagyeman/openmv,iabdalkader/openmv,iabdalkader/openmv,openmv/openmv,iabdalkader/openmv,openmv/openmv,kwagyeman/openmv,openmv/openmv,iabdalkader/openmv,openmv/openmv,kwagyeman/openmv