fixed some inconsistencies in the document

docs/run_demo.md

@@ -19,41 +19,54 @@ where `HOST` is the IP address of your system. Note that we use
 the [Slurm](https://slurm.schedmd.com/documentation.html) job scheduling system here.
 
 ```bash
-HOST=xxx.xxx.xxx.xxx srun ./scripts/slurm_dist_train.sh ./example/train_vit_2d.py ./configs/vit/vit_2d.py
+HOST=xxx.xxx.xxx.xxx srun ./scripts/slurm_dist_train.sh ./examples/run_trainer.py ./configs/vit/vit_2d.py
 ```
 
 `./configs/vit/vit_2d.py` is a config file, which is introduced in the [Config file](config.md) section below. These
 config files are used by ColossalAI to define all kinds of training arguments, such as the model, dataset and training
 method (optimizer, lr_scheduler, epoch, etc.). Config files are highly customizable and can be modified so as to train
 different models.
-`./example/run_trainer.py` contains a standard training script and is presented below, it reads the config file and
+`./examples/run_trainer.py` contains a standard training script and is presented below, it reads the config file and
 realizes the training process.
 
 ```python
 import colossalai
+from colossalai.core import global_context as gpc
 from colossalai.engine import Engine
+from colossalai.logging import get_global_dist_logger
 from colossalai.trainer import Trainer
-from colossalai.core import global_context as gpc
 
-model, train_dataloader, test_dataloader, criterion, optimizer, schedule, lr_scheduler = colossalai.initialize()
-engine = Engine(
-    model=model,
-    criterion=criterion,
-    optimizer=optimizer,
-    lr_scheduler=lr_scheduler,
-    schedule=schedule
-)
-
-trainer = Trainer(engine=engine,
-                  hooks_cfg=gpc.config.hooks,
-                  verbose=True)
-trainer.fit(
-    train_dataloader=train_dataloader,
-    test_dataloader=test_dataloader,
-    max_epochs=gpc.config.num_epochs,
-    display_progress=True,
-    test_interval=5
-)
+
+def run_trainer():
+    model, train_dataloader, test_dataloader, criterion, optimizer, schedule, lr_scheduler = colossalai.initialize()
+    logger = get_global_dist_logger()
+    schedule.data_sync = False
+    engine = Engine(
+        model=model,
+        criterion=criterion,
+        optimizer=optimizer,
+        lr_scheduler=lr_scheduler,
+        schedule=schedule
+    )
+    logger.info("engine is built", ranks=[0])
+
+    trainer = Trainer(engine=engine,
+                      hooks_cfg=gpc.config.hooks,
+                      verbose=True)
+    logger.info("trainer is built", ranks=[0])
+
+    logger.info("start training", ranks=[0])
+    trainer.fit(
+        train_dataloader=train_dataloader,
+        test_dataloader=test_dataloader,
+        max_epochs=gpc.config.num_epochs,
+        display_progress=True,
+        test_interval=2
+    )
+
+
+if __name__ == '__main__':
+    run_trainer()
 ```
 
 Alternatively, the `model` variable can be substituted with a self-defined model or a pre-defined model in our Model