Documentation of DataCollatorForLanguageModeling
# 🚀 Feature request

Would you consider adding to the following tip:

"For best performance, this data collator should be used with a dataset having items that are dictionaries or BatchEncoding, with the "special_tokens_mask" key, ...."

The reason for doing so, for example: "So that special mask tokens won't be masked".

Hey! Would you like to open a PR?<|||||>Yes, I'll do that<|||||>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/main/CONTRIBUTING.md) are likely to be ignored.