Arxiv README (#2747)

* Arxiv README

* ArXiv-NLP readme

model_cards/lysandre/arxiv-nlp/README.md

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+# ArXiv-NLP GPT-2 checkpoint
+
+This is a GPT-2 small checkpoint for PyTorch. It is the official `gpt2-small` fine-tuned to ArXiv paper on the computational linguistics field.
+
+## Training data
+
+This model was trained on a subset of ArXiv papers that were parsed from PDF to txt. The resulting data is made of 80MB of text from the computational linguistics (cs.CL) field.