doc: refactor using_sklearn and fix minor errors in using_pytorch and using_chainer (#985)

Refactored "Using Scikit-learn" topic in doc project, and made minor updates to "Using PyTorch" and "Using Chainer" topics.

Author: eslesar-aws

doc/using_chainer.rst

@@ -4,9 +4,9 @@ Using Chainer with the SageMaker Python SDK
 
 With Chainer Estimators, you can train and host Chainer models on Amazon SageMaker.
 
-Supported versions of Chainer: ``4.0.0``, ``4.1.0``, ``5.0.0``
+For information about supported versions of Chainer, see the `Chainer README <https://github.com/aws/sagemaker-python-sdk/blob/master/src/sagemaker/chainer/README.rst>`__.
 
-You can visit the Chainer repository at https://github.com/chainer/chainer.
+For general information about using the SageMaker Python SDK, see :ref:`overview:Using the SageMaker Python SDK`.
 
 .. contents::
 
@@ -635,6 +635,6 @@ The following are optional arguments. When you create a ``Chainer`` object, you
 SageMaker Chainer Docker containers
 ***********************************
 
-You can visit the SageMaker Chainer containers repository here: https://github.com/aws/sagemaker-chainer-containers/
+You can visit the SageMaker Chainer containers repository here: https://github.com/aws/sagemaker-chainer-container
 
-For information about SageMaker TensorFlow Docker containers and their dependencies, see `SageMaker Chainer Docker containers <https://github.com/aws/sagemaker-python-sdk/tree/master/src/sagemaker/chainer#sagemaker-chainer-docker-containers>`_.
+For information about SageMaker Chainer Docker containers and their dependencies, see `SageMaker Chainer Docker containers <https://github.com/aws/sagemaker-python-sdk/tree/master/src/sagemaker/chainer#sagemaker-chainer-docker-containers>`_.

doc/using_pytorch.rst

@@ -658,6 +658,6 @@ The following are optional arguments. When you create a ``PyTorch`` object, you
 SageMaker PyTorch Docker Containers 
 ***********************************
 
-For information about SageMaker PyTorch containers, see  `the SageMaker PyTorch containers repository <https://github.com/aws/sagemaker-pytorch-containers>`_.
+For information about SageMaker PyTorch containers, see  `the SageMaker PyTorch containers repository <https://github.com/aws/sagemaker-pytorch-container>`_.
 
 For information about SageMaker PyTorch container dependencies, see `SageMaker PyTorch Containers <https://github.com/aws/sagemaker-python-sdk/tree/master/src/sagemaker/pytorch#sagemaker-pytorch-docker-containers>`_.