update readme

README.md

@@ -44,11 +44,15 @@ labels = torch.tensor([0]) # 1 batch
 # focal loss
 focal_loss = Loss(loss_type="focal_loss")
 loss = focal_loss(logits, labels)
+```
 
+```python
 # cross-entropy loss
 ce_loss = Loss(loss_type="cross_entropy")
 loss = ce_loss(logits, labels)
+```
 
+```python
 # binary cross-entropy loss
 bce_loss = Loss(loss_type="binary_cross_entropy")
 loss = bce_loss(logits, labels)
@@ -74,15 +78,19 @@ focal_loss = Loss(
     class_balanced=True
 )
 loss = focal_loss(logits, labels)
+```
 
+```python
 # class-balanced cross-entropy loss
 ce_loss = Loss(
     loss_type="cross_entropy",
     samples_per_class=samples_per_class,
     class_balanced=True
 )
 loss = ce_loss(logits, labels)
+```
 
+```python
 # class-balanced binary cross-entropy loss
 bce_loss = Loss(
     loss_type="binary_cross_entropy",