SecurityPolicyDsc: Add DSCResource README.md files

[X-Guardian]

Pull Request (PR) description

This PR adds README.md description files to each Dsc resource.

This Pull Request (PR) fixes the following issues

None

Task list

• [ ] Added an entry under the Unreleased section of the change log in the CHANGELOG.md. Entry should say what was changed, and how that affects users (if applicable).
• [x] Resource documentation added/updated in README.md.
• [ ] Resource parameter descriptions added/updated in README.md, schema.mof and comment-based help.
• [ ] Comment-based help added/updated.
• [ ] Localization strings added/updated in all localization files as appropriate.
• [ ] Examples appropriately added/updated.
• [ ] Unit tests added/updated. See DSC Resource Testing Guidelines.
• [ ] Integration tests added/updated (where possible). See DSC Resource Testing Guidelines.
• [ ] New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

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This change is 

[codecov-io]

Codecov Report

Merging #138 into dev will not change coverage. The diff coverage is n/a.

@@        Coverage Diff         @@
##           dev   #138   +/-   ##
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  Coverage   90%    90%           
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  Files        5      5           
  Lines      573    573           
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  Hits       521    521           
  Misses      52     52