Adding documentation for utility functions (#205)

Summary:
Pull Request resolved: #205

Setup documentation for utility function and added some links to PyTorch Core documentation.

Let me know what else should be added here.

Test Plan: Imported from OSS

Reviewed By: VitalyFedyunin, ejguan

Differential Revision: D34093684

Pulled By: NivekT

fbshipit-source-id: b6e1a3c111570140c5a3ae8c6a5f0a4ec15d8303

Author: NivekT

docs/source/torchdata.datapipes.iter.rst

@@ -101,7 +101,6 @@ These DataPipes provide utility functions (e.g. caching, CSV parsing, filtering)
     InMemoryCacheHolder
     IndexAdder
     IoPathSaver
-    IterDataPipe
     IterKeyZipper
     IterableWrapper
     JsonParser

docs/source/torchdata.datapipes.utils.rst

@@ -1,6 +1,32 @@
 Utility Functions
 ===========================
 
-.. currentmodule:: torchdata.datapipes.util
+File Object and Stream Utility
+-------------------------------------
 
-Coming soon!
+.. currentmodule:: torchdata.datapipes.utils
+
+.. autosummary::
+    :nosignatures:
+    :toctree: generated/
+    :template: datapipe.rst
+
+    StreamWrapper
+
+
+DataLoader
+-------------------------------------
+
+For documentation related to DataLoader, please refer to the
+``torch.utils.data`` `documentation <https://pytorch.org/docs/stable/data.html>`_. Or, more specifically, the
+`DataLoader API section <https://pytorch.org/docs/stable/data.html#torch.utils.data.DataLoader>`_.
+
+DataLoader v2 is currently in development. You should see an update here by mid-2022.
+
+Sampler
+-------------------------------------
+
+For documentation related to Sampler, please refer to the
+``torch.utils.data``
+`documentation on Data Loading order <https://pytorch.org/docs/stable/data.html#data-loading-order-and-sampler>`_.
+The Sampler API section is `here <https://pytorch.org/docs/stable/data.html#torch.utils.data.Sampler>`_.