Fix log message for training from checkpoint with global step
# 🚀 Feature request

I think the log message here is wrong:

https://github.com/huggingface/transformers/blob/master/src/transformers/trainer.py#L978

I think it should read something along these lines:

```
logger.info(
                    f"  Will skip the first {epochs_trained} epochs then the first {steps_trained_in_current_epoch} "
                    "batches in the current epoch {epochs_trained + 1}."
                )
```

The batches that are skipped are not skipped in the first epoch since the training was already done for `epochs_trained`. As the variable name indicates, the training is going to skip the steps already trained in the current epoch. The current epoch is `epochs_trained + 1`. 

## Motivation

The log message was confusing. I went and traced the code to ensure that it does the right skipping (which I think it does). 
Yes, that sounds clearer. Would you mind making a PR with this?<|||||>Will make time this week. <|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.