add comment to custom_collate fn

src/rydberggpt/data/dataclasses.py

@@ -46,6 +46,10 @@ def custom_collate(batch: List[Batch]) -> Batch:
 
     graph_batch = PyGBatch.from_data_list([b.graph for b in batch])
 
+    # NOTE: The graphs, and measurement data are not of the same size. To ensure
+    # a padded tensor suitable for the neural network, we use the to_dense_batch function. This ensures that our
+    # data is padded with zeros.
+    # see: https://pytorch-geometric.readthedocs.io/en/latest/_modules/torch_geometric/utils/to_dense_batch.html
     batch = Batch(
         graph=graph_batch,
         m_onehot=to_dense_batch(