Outdated README: play progress and supports animation features

[Dario-Gasquez]

The README file uses this code sample:

self.waveform.progressSamples = self.waveform.totalSamples / 2

To illustrate the Set play progress feature (also applies to the Supports animation feature).

Latest code version requires something like this:

let samplesToHighlight = waveformView.totalSamples / 2
 waveformView.highlightedSamples = 0 ..< samplesToHighlight

Suggestion:
Update the README to reflect this code change.

[fulldecent]

Confirmed defect. Thank you.