fixed the example docstring for booster (#3795)

colossalai/booster/booster.py

@@ -23,27 +23,28 @@ class Booster:
     training with different precision, accelerator, and plugin.
 
     Examples:
-        >>> colossalai.launch(...)
-        >>> plugin = GeminiPlugin(stage=3, ...)
-        >>> booster = Booster(precision='fp16', plugin=plugin)
-        >>>
-        >>> model = GPT2()
-        >>> optimizer = Adam(model.parameters())
-        >>> dataloader = Dataloader(Dataset)
-        >>> lr_scheduler = LinearWarmupScheduler()
-        >>> criterion = GPTLMLoss()
-        >>>
-        >>> model, optimizer, lr_scheduler, dataloader = booster.boost(model, optimizer, lr_scheduler, dataloader)
-        >>>
-        >>> for epoch in range(max_epochs):
-        >>>     for input_ids, attention_mask in dataloader:
-        >>>         outputs = model(input_ids, attention_mask)
-        >>>         loss = criterion(outputs.logits, input_ids)
-        >>>         booster.backward(loss, optimizer)
-        >>>         optimizer.step()
-        >>>         lr_scheduler.step()
-        >>>         optimizer.zero_grad()
-
+        ```python
+        colossalai.launch(...)
+        plugin = GeminiPlugin(stage=3, ...)
+        booster = Booster(precision='fp16', plugin=plugin)
+
+        model = GPT2()
+        optimizer = Adam(model.parameters())
+        dataloader = Dataloader(Dataset)
+        lr_scheduler = LinearWarmupScheduler()
+        criterion = GPTLMLoss()
+
+        model, optimizer, lr_scheduler, dataloader = booster.boost(model, optimizer, lr_scheduler, dataloader)
+
+        for epoch in range(max_epochs):
+            for input_ids, attention_mask in dataloader:
+                outputs = model(input_ids, attention_mask)
+                loss = criterion(outputs.logits, input_ids)
+                booster.backward(loss, optimizer)
+                optimizer.step()
+                lr_scheduler.step()
+                optimizer.zero_grad()
+        ```
 
     Args:
         device (str or torch.device): The device to run the training. Default: 'cuda'.