Add modelcard for Hate-speech-CNERG/dehatebert-mono-arabic model (#3979)

* Add dehatebert-mono-arabic readme card

* Update dehatebert-mono-arabic model card

model_cards/Hate-speech-CNERG/dehatebert-mono-arabic/README.md

+This model is used detecting **hatespeech** in **Arabic language**. The mono in the name refers to the monolingual setting, where the model is trained using only Arabic language data. It is finetuned on multilingual bert model.
+The model is trained with different learning rates and the best validation score achieved is 0.8674776 for a learning rate of 2e-5. Training code can be found at this [url](https://github.com/punyajoy/DE-LIMIT)