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/nikokons/gpt2-greek/README.md

README.md

@@ -0,0 +1,5 @@
+---
+language: el
+---
+
+## gpt2-greek