Errors in Quickstart  Documentation related to GPT-2
Author: williamsdoug
Pull request: no

To: @sgugger, @patrickvonplaten, @LysandreJik


## Environment info

- `transformers` version: 4.6.0
- Platform: Linux-5.4.0-73-generic-x86_64-with-glibc2.10
- Python version: 3.8.5
- PyTorch version (GPU?): 1.8.1 (True)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: True
- Using distributed or parallel set-up in script?: False

### Who can help
@sgugger, @patrickvonplaten, @LysandreJik

## Information

Model I am using (gpt-2 ...):

The problem arises when using:
* Example code in **Quickstart** page on online [documentation](https://huggingface.co/transformers/quickstart.html) section **OpenAI GPT-2** / **Using the past**

### Existing Code
```
for i in range(100):
    print(i)
    output, past = model(context, past=past)
    token = torch.argmax(output[..., -1, :])

    generated += [token.tolist()]
    context = token.unsqueeze(0)

sequence = tokenizer.decode(generated)

print(sequence)
```

### Errors Encountered in statement ```output, past = model(context, past=past)```

-  Obsolete named parameter **past**, replaced by **past_key_values** in current release
-  Assignment to ```output, past =``` does not assign expected values
   - model() statement returns value of type ```transformers.modeling_outputs.CausalLMOutputWithCrossAttentions``` 


### Suggested Corrected Version

```
for i in range(100):
    print(i)
    ret = model(context, past_key_values=past)
    output, past = ret.logits, ret.past_key_values
    # or
    # output, past = ret[0], ret[1]
    token = torch.argmax(output[..., -1, :])

    generated += [token.tolist()]
    context = token.unsqueeze(0)

sequence = tokenizer.decode(generated)

print(sequence)
```


Comments:
Oh, this page should not be there anymore, it's part of the old documentation. Out of curiosity, how did you get on it?

Hi @sgugger -

I think I see the problem.  If the user navigates to huggingface.co first, then follows the links, it points to the updated documentation.  Also, the link associated with the Transformers github repo points to the current docs..

However, if the user navigates via a Google search and clicks on Quickstart, it redirects to  an obsolete version of the docs.  See screenshot attached.

![Screenshot from 2021-05-25 15-30-02](https://user-images.githubusercontent.com/2381871/119558029-ec184d80-bd6e-11eb-8308-699f3f4fa2e8.png)


I have removed the page from the doc website. Hopefully Google will update its recommendation soon!

Note that there probably are some SEO-related optimisations to our doc site layout to make sure Sitelinks are kept up-to-date (and the latest released version is the one best ranked by Google):

https://support.google.com/webmasters/answer/47334?hl=en

In terms of UX, one can also display a banner on top on the doc for every non-latest version. cc @gary149 

Note that here it was trying to render that file in the current version (the version selector said stable doc for instance), so it was really confusing.

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.