Improved TaleaRhythmMaker docs.

Added detailed example for TaleaRhythmMaker.prolation_addenda.

The property adds extra counts cyclically to the durations talea rhythm-makers
make.

(Maybe prolation_addenda should be called extra_counts_per_division.)

Note that both TaleaRhythmMaker and IncisedRhythmMaker implement
prolation_addenda.