Confused by config parameters among total_steps, epochs, batch_size and num_rollouts

### 📚 The doc issue

TrainConfig has some general explanation about some of the parameters. But after running the [ppo_hh.py](https://github.com/CarperAI/trlx/blob/main/examples/hh/ppo_hh.py), i got confused.
1. ppo_hh.py set total_steps and epochs while it seems epochs was ignored in the training.
2. How many data will a step consumed? num_rollout or batch_size?
3. In my understanding, every epoch uses num_rollout examples. They are used for generation in a chunk_size batch. Then every step use batch_size to update the policy model. Am i right?

Thank you in advance for answering all the questions.

### Suggest a potential alternative/fix

Maybe there should be some more detailed description about these parameters?