readme: Fine tuning LayoutLMv2 model on Vietnamese bill dataset 
  ```python
  from transformers import LayoutLMv2ForTokenClassification
  model = LayoutLMv2ForTokenClassification.from_pretrained('cuongngm/layoutlm-bill', num_labels=len(labels))
  ```
  
  labels = ['price',
   'storename',
   'total_cost',
   'phone',
   'address',
   'unitprice',
   'item',
   'subitem',
   'other',
   'time',
   'unit',
   'total refunds',
   'total_qty',
   'seller',
   'total_received']