Miscellaneous documentation improvements: (#868)

Summary:
- More clearly document the correspondence between FairseqAdam and torch.optim.AdamW
- Add ResamplingDataset to Sphinx docs
Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/868

Differential Revision: D17523244

Pulled By: jma127

fbshipit-source-id: 8e7b34b24889b2c8f70b09a52a625d2af135734b

docs/data.rst

@@ -30,6 +30,8 @@ provide additional functionality:
     :members:
 .. autoclass:: fairseq.data.ConcatDataset
     :members:
+.. autoclass:: fairseq.data.ResamplingDataset
+    :members:
 .. autoclass:: fairseq.data.RoundRobinZipDatasets
     :members:
 .. autoclass:: fairseq.data.TransformEosDataset

fairseq/optim/adam.py

@@ -15,6 +15,12 @@ from . import FairseqOptimizer, register_optimizer
 
 @register_optimizer('adam')
 class FairseqAdam(FairseqOptimizer):
+    """Adam optimizer for fairseq.
+
+    Important note: this optimizer corresponds to the "AdamW" variant of
+    Adam in its weight decay behavior. As such, it is most closely
+    analogous to torch.optim.AdamW from PyTorch.
+    """
 
     def __init__(self, args, params):
         super().__init__(args)