fix: update sagemaker pytorch containers to external link (#1409)

Author: chuyang-deng

doc/using_pytorch.rst

@@ -134,7 +134,7 @@ Using third-party libraries
 ---------------------------
 
 When running your training script on SageMaker, it will have access to some pre-installed third-party libraries including ``torch``, ``torchvision``, and ``numpy``.
-For more information on the runtime environment, including specific package versions, see `SageMaker PyTorch Docker containers <#id4>`__.
+For more information on the runtime environment, including specific package versions, see `SageMaker PyTorch Docker containers <https://github.com/aws/sagemaker-python-sdk/tree/master/src/sagemaker/pytorch#sagemaker-pytorch-docker-containers>`_.
 
 If there are other packages you want to use with your script, you can include a ``requirements.txt`` file in the same directory as your training script to install other dependencies at runtime. Both ``requirements.txt`` and your training script should be put in the same folder. You must specify this folder in ``source_dir`` argument when creating PyTorch estimator.
 
@@ -673,7 +673,7 @@ The following are optional arguments. When you create a ``PyTorch`` object, you
    model training code.
 -  ``framework_version`` PyTorch version you want to use for executing
    your model training code. You can find the list of supported versions
-   in `SageMaker PyTorch Docker Containers <#id4>`_.
+   in `SageMaker PyTorch Docker Containers <https://github.com/aws/sagemaker-python-sdk/tree/master/src/sagemaker/pytorch#sagemaker-pytorch-docker-containers>`_.
 -  ``train_volume_size`` Size in GB of the EBS volume to use for storing
    input data during training. Must be large enough to store training
    data if input_mode='File' is used (which is the default).
@@ -698,7 +698,7 @@ The following are optional arguments. When you create a ``PyTorch`` object, you
    serving.  If specified, the estimator will use this image for training and
    hosting, instead of selecting the appropriate SageMaker official image based on
    framework_version and py_version. Refer to: `SageMaker PyTorch Docker Containers
-   <#id4>`_ for details on what the Official images support
+   <https://github.com/aws/sagemaker-python-sdk/tree/master/src/sagemaker/pytorch#sagemaker-pytorch-docker-containers>`_ for details on what the Official images support
    and where to find the source code to build your custom image.
 
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