Add resample example

[wiccy46]

The documentation is not obvious regarding how to resample an input.

[dvdsk]

The sink will resample input for you when you append see:

rodio/src/sink.rs

Line 150 in 818f557

.convert_samples();

This example is therefore resampling twice (once using UniformSourceIterator explicit and once implicit in sink). That does not make sense right?

A PR clarifying the docs for Sink::append might be a better way to address this. Cause I do agree it is very confusing and not obvious how input is resampled! Please, if you are willing, help improve the docs, we could really use the help.