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/iarfmoose/roberta-base-bulgarian/README.md

README.md

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+---
+language: bg
+---
+
+# RoBERTa-base-bulgarian
+
+
+The RoBERTa model was originally introduced in [this paper](https://arxiv.org/abs/1907.11692). This is a version of [RoBERTa-base](https://huggingface.co/roberta-base) pretrained on Bulgarian text.
+
+## Intended uses
+
+This model can be used for cloze tasks (masked language modeling) or finetuned on other tasks in Bulgarian.
+
+## Limitations and bias
+
+The training data is unfiltered text from the internet and may contain all sorts of biases.
+
+## Training data
+
+This model was trained on the following data:
+- [bg_dedup from OSCAR](https://oscar-corpus.com/)
+- [Newscrawl 1 million sentences 2017 from Leipzig Corpora Collection](https://wortschatz.uni-leipzig.de/en/download/bulgarian)
+- [Wikipedia 1 million sentences 2016 from Leipzig Corpora Collection](https://wortschatz.uni-leipzig.de/en/download/bulgarian)
+
+## Training procedure
+
+The model was pretrained using a masked language-modeling objective with dynamic masking as described [here](https://huggingface.co/roberta-base#preprocessing)
+
+It was trained for 200k steps. The batch size was limited to 8 due to GPU memory limitations.