add example of self-supervised SimCLR training - V2 (#50)

* add example of self-supervised SimCLR training

* simclr v2, replace nvidia dali dataloader

* updated

* sync to latest code writing style

* sync to latest code writing style and modify README

* detail README & standardize dataset path

examples/simclr_cifar10_data_parallel/myhooks.py

@@ -0,0 +1,15 @@
+from colossalai.trainer.hooks import BaseHook
+from colossalai.core import global_context as gpc
+from colossalai.context import ParallelMode
+from colossalai.logging import get_dist_logger
+
+
+class TotalBatchsizeHook(BaseHook):
+    def __init__(self, priority: int = 2) -> None:
+        super().__init__(priority)
+        self.logger = get_dist_logger()
+
+    def before_train(self, trainer):
+        total_batch_size = gpc.config.BATCH_SIZE * \
+            gpc.config.gradient_accumulation * gpc.get_world_size(ParallelMode.DATA)
+        self.logger.info(f'Total batch size = {total_batch_size}', ranks=[0])