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/moumeneb1/flaubert-base-cased-ecology_crisis/README.md

README.md

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+# Flaubert-base-cased-ecology_crisis
+
+An adapted [__Flaubert/Flaubert_base-cased model__](https://github.com/getalp/Flaubert) Trained further on a Language modeling Task of unlabeled French tweets used to create the [CrisisDataset](https://github.com/DiegoKoz/french_ecological_crisis), The intermediate task of masqued language modeling helped us improve the results on our [paper](http://www.sciencedirect.com/science/article/pii/S0306457320300650) compared to the standard flaubert-base-cased model.
+
+If you use this pretrained model on your work, please cite us as follows 🤗
+
+```
+@article{Kozlowski-et-al2020,
+title = "A three-level classification of French tweets in ecological crises",
+journal = "Information Processing & Management",
+volume = "57",
+number = "5",
+pages = "102284",
+year = "2020",
+issn = "0306-4573",
+doi = "https://doi.org/10.1016/j.ipm.2020.102284",
+url = "http://www.sciencedirect.com/science/article/pii/S0306457320300650",
+author = "Diego Kozlowski and Elisa Lannelongue and Frédéric Saudemont and Farah Benamara and Alda Mari and Véronique Moriceau and Abdelmoumene Boumadane",
+keywords = "Crisis response from social media, Machine learning, Natural language processing, Transfer learning",
+}
+
+```
+