use_fast=False when loading OPT's tokenizer?
### System Info

platform==Ubuntu 18.04.01
python==3.10
transformers==4.29.1

### Who can help?

@sgugger @stevhliu @MK

### Information

- [ ] The official example scripts
- [ ] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

It is shown in the OPT model [documentation](https://huggingface.co/docs/transformers/model_doc/opt) (in Tips) that it is required to pass `use_fast=False` when loading a OPT tokenizer, as OPT tokenizer will add `</s>` to the beginning of every prompt.

I made a trial:
```python
>>> import transformers
>>> tokenizer = transformers.AutoTokenizer.from_pretrained("facebook/opt-1.3b", use_fast=False)
>>> tokenizer_fast = transformers.AutoTokenizer.from_pretrained("facebook/opt-1.3b", use_fast=True)
>>> text = "I like you."
>>> tokenizer(text)
>>> {'input_ids': [2, 100, 101, 47, 4], 'attention_mask': [1, 1, 1, 1, 1]}
>>> tokenizer_fast(text)
>>> {'input_ids': [2, 100, 101, 47, 4], 'attention_mask': [1, 1, 1, 1, 1]}
```

`</s>` is correctly added and no difference is observed.

### Expected behavior

Is the tips wrong or in some other cases `use_fast=Fast` is actually required?
cc @ArthurZucker <|||||>Hey! Thanks for reporting. Pretty sure the doc is wrong, but `use_fast=True` use to not be supported for OPT, which could explain this. 