Fixed typos in readme files of docs folder.

[rishit5]

What does this PR do?

Fixes all the typos of the readme files in the docs folder

Fixes # (issue)

Fixed typos in the following files:

1. docs/source/basic_tutorials/notebook.md
2. docs/source/concept_guides/low_precision_training.md
3. docs/source/package_reference/cli.md
4. docs/source/package_reference/utilities.md
5. docs/source/usage_guides/big_modeling.md
6. docs/source/usage_guides/deepspeed.md
7. docs/source/usage_guides/fsdp.md
8. docs/source/usage_guides/low_precision_training.md
9. docs/source/usage_guides/megatron_lm.md

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

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[muellerzr]

Thanks for your contribution!

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