add model description

README.md

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+---
+language:
+- en
+base_model:
+- allenai/longformer-large-4096
+---
+This is the fine-tuned version of the `longformer-large-4096` model additionally pre-trained on the S2ORC corpus [(Lo et al., 2020)](https://arxiv.org/pdf/1911.02782), which is a large corpus of 81.1M English-language academic papers from different disciplines. This model uses the weights of [the longformer large science checkpoint](https://github.com/dwadden/multivers/blob/main/script/get_checkpoint.py) that was used as the starting point for training the MultiVerS model [(Wadden et al., 2022)](https://arxiv.org/pdf/2112.01640) on the task of scientific claim verification.
+
+Note that the vocabulary size of this model (50275) differs from the original `longformer-large-4096` (50265) since 10 new tokens were included:
+
+`<|par|>, </|title|>, </|sec|>, <|sec-title|>, <|sent|>, <|title|>, <|abs|>, <|sec|>, </|sec-title|>, </|abs|>`.