Not enough documentation for EpisodeAdder

Having read the [docs](https://github.com/deepmind/acme/blob/master/docs/components.md) and the code for the [episode adder](https://github.com/deepmind/acme/blob/master/acme/adders/reverb/episode.py#L51) I still don't quite understand it.

Is it just the simplest adder? E.g. adding every transition to one long buffer? Or is it doing something else?

Thanks!