added model card

README.md

@@ -32,8 +32,10 @@ For example, assuming we want to finetune this model on a token classification t
 
 ```python
 >>> from transformers import AutoTokenizer, AutoModelForTokenClassification
->>> tokenizer = AutoTokenizer.from_pretrained("castorini/afriberta_small")
 >>> model = AutoModelForTokenClassification.from_pretrained("castorini/afriberta_small")
+>>> tokenizer = AutoTokenizer.from_pretrained("castorini/afriberta_small")
+# we have to manually set the model max length because it is an imported sentencepiece model which hugginface does not properly support right now
+>>> tokenizer.model_max_length = 512 
 ```
 
 #### Limitations and bias