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/distilbert-base-cased-distilled-squad-README.md

README.md

@@ -0,0 +1,13 @@
+---
+language: "en"
+datasets:
+- squad
+metrics:
+- squad
+license: apache-2.0
+---
+
+# DistilBERT base cased distilled SQuAD
+
+This model is a fine-tune checkpoint of [DistilBERT-base-cased](https://huggingface.co/distilbert-base-cased), fine-tuned using (a second step of) knowledge distillation on SQuAD v1.1.
+This model reaches a F1 score of 87.1 on the dev set (for comparison, BERT bert-base-cased version reaches a F1 score of 88.7).