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/keshan/SinhalaBERTo/README.md

README.md

@@ -0,0 +1,37 @@
+---
+language: si
+tags:
+- SinhalaBERTo
+- Sinhala
+- roberta
+datasets:
+- oscar
+---
+### Overview
+
+This is a slightly smaller model trained on [OSCAR](https://oscar-corpus.com/) Sinhala dedup dataset. As Sinhala is one of those low resource languages, there are only a handful of models been trained. So, this would be a great place to start training for more downstream tasks. 
+
+## Model Specification
+
+
+The model chosen for training is [Roberta](https://arxiv.org/abs/1907.11692) with the following specifications:
+ 1. vocab_size=52000
+ 2. max_position_embeddings=514
+ 3. num_attention_heads=12
+ 4. num_hidden_layers=6
+ 5. type_vocab_size=1
+ 
+## How to Use
+You can use this model directly with a pipeline for masked language modeling:
+
+```py
+from transformers import AutoTokenizer, AutoModelWithLMHead, pipeline
+
+model = BertForMaskedLM.from_pretrained("keshan/SinhalaBERTo")
+tokenizer = BertTokenizer.from_pretrained("keshan/SinhalaBERTo")
+
+fill_mask = pipeline('fill-mask', model=model, tokenizer=tokenizer)
+
+fill_mask("මම ගෙදර <mask>.")
+
+```