Migrate model card from transformers-repo

Read announcement at https://discuss.huggingface.co/t/announcement-all-model-cards-will-be-migrated-to-hf-co-model-repos/2755
Original file history: https://github.com/huggingface/transformers/commits/master/model_cards/roberta-large-mnli-README.md

README.md

@@ -0,0 +1,22 @@
+---
+license: mit
+widget:
+- text: "I like you. </s></s> I love you."
+---
+
+
+## roberta-large-mnli
+
+Trained by Facebook, [original source](https://github.com/pytorch/fairseq/tree/master/examples/roberta)
+
+```bibtex
+@article{liu2019roberta,
+    title = {RoBERTa: A Robustly Optimized BERT Pretraining Approach},
+    author = {Yinhan Liu and Myle Ott and Naman Goyal and Jingfei Du and
+              Mandar Joshi and Danqi Chen and Omer Levy and Mike Lewis and
+              Luke Zettlemoyer and Veselin Stoyanov},
+    journal={arXiv preprint arXiv:1907.11692},
+    year = {2019},
+}
+```
+