Feat: Update readme for distributed optimize

[deependujha]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

• Readme updated for Distributed Optimize function
• more tests added for resuming dataloader from a checkpoint

PR review

Anyone in the community is free to review the PR once the tests have passed.
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[codecov]

Codecov Report

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Additional details and impacted files

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