3405 Enhance doc-string of MIL model for data shape

monai/networks/nets/milmodel.py

@@ -11,6 +11,11 @@
 class MILModel(nn.Module):
     """
     Multiple Instance Learning (MIL) model, with a backbone classification model.
+    Currently, it only works for 2D images, typical use case is for classification of the
+    digital pathology whole slide images. The expected shape of input data is `[B, N, C, H, W]`,
+    where `B` is the batch_size of PyTorch Dataloader and `N` is the number of the instances
+    extracted from every original image in the batch. A tutorial example is available at:
+    https://github.com/Project-MONAI/tutorials/tree/master/pathology/multiple_instance_learning.
 
     Args:
         num_classes: number of output classes.