Add note for WikiSplit

Author: patrickvonplaten

model_cards/google/roberta2roberta_L-24_wikisplit/README.md

@@ -17,6 +17,9 @@ Disclaimer: The model card has been written by the Hugging Face team.
 
 You can use this model for sentence splitting, *e.g.*
 
+**IMPORTANT**: The model was not trained on the `"` (double quotation mark) character -> so the before tokenizing the text, 
+it is advised to replace all `"` (double quotation marks) with two single `'` (single quotation mark).
+
 ```python
 from transformers import AutoTokenizer, AutoModelForSeq2SeqLM