Fix docs for decoder_input_ids in BART.
Fix docs for `decoder_input_ids` in BART.
Fix #15691
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15697). All of your documentation changes will be reflected on that endpoint.<|||||>Done.
Please review again.<|||||>Thanks! However, as you can see, the CI needs all checks passing before we can merge this PR.

For this to pass, you need to run `make fixup` locally and make sure all quality and style checks pass. For more information, please read [this guide](https://huggingface.co/docs/transformers/contributing).

<img width="943" alt="Screenshot 2022-02-18 at 11 28 45" src="https://user-images.githubusercontent.com/48327001/154672136-9cb64b92-d785-4f7e-8b2e-ee9ca8060ebe.png">

<|||||>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.