message: More explanation to vvgpu
  Update python interface.md to fix
diff: @@ -102,7 +102,7 @@ hugectr.CreateSolver()
  * `batchsize`: Minibatch size used in training. The default value is 2048. **Note that batchsize here is the global batch size across gpus and nodes , not per worker batch size.**
  -* `vvgpu`: GPU indices used in the training process, which has two levels. For example: [[0,1],[1,2]] indicates that two nodes are used. In the first node, GPUs 0 and 1 are used while GPUs 1 and 2 are used for the second node. It is also possible to specify non-continuous GPU indices such as [0, 2, 4, 7]. The default value is [[0]].
  +* `vvgpu`: GPU indices used in the training process, which has two levels. For example: [[0,1],[1,2]] indicates that two physical nodes (each physical node can have multiple NUMA nodes) are used. In the first node, GPUs 0 and 1 are used while GPUs 1 and 2 are used for the second node. It is also possible to specify non-continuous GPU indices such as [0, 2, 4, 7]. The default value is [[0]].
  * `repeat_dataset`: Whether to repeat the dataset for training. If the value is `True`, non-epoch mode training will be employed. Otherwise, epoch mode training will be adopted. The default value is `True`.
  