Updated distributed_training.md

[NihalHarish]

Description of changes:

• Updated docs : docs/distributed_training.md
• Currently still WIP: Need to add docs and examples for XGBoost
• More examples to cover missing cases.
  • TF 1.x Horovod
  • TF 1.x Mirrored Strategy
  • TF 2.x Horovod Keras Fit API
  • TF 2.x Horovod Gradient Tape API
  • TF 2.x Mirrored Strategy
  • Pytorch Horovod Example
  • Pytorch distributed training
  • Mxnet Horovod

Style and formatting:

I have run pre-commit install to ensure that auto-formatting happens with every commit.

Issue number, if available

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[Vikas-kum]

@NihalHarish Please make the changes that we discussed last week offline.

[NihalHarish]

@NihalHarish Please make the changes that we discussed last week offline.

Changes discussed offline: Remove ZCC examples that need additional configuration,