Run stepper motor for a precise number of steps.

[gsabran]

Would it be possible to provide examples for how to use pigpio for a stepper motor in the ReadMe 🙏 ? This issue was raised in the past (https://github.com/fivdi/pigpio/issues/88) at a time where waveforms were not supported. They are now (https://github.com/fivdi/pigpio/pull/95) 🎉! It's however unclear to me how one would use waveforms to write code such as this python example.