Create PLACEHOLDER.md

[tenthirtyam]

Placeholder to address missing manifests folder.

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Summary of Pull Request

Adding a placeholder for the manifests directory.

Type of Pull Request

• This is a bug fix.
• This is an enhancement or feature.
• This is a code style / formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is a something else.
  Please describe:

Context of the Pull Request*

Adding a placeholder for the manifests directory.

Related to Existing Issues

Issue Number: 36
Closes: 36

Test and Documentation Coverage

• Tests have been been completed (for bug fixes / features).
• Documentation has been added / updated (for bug fixes / features).

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues. If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.