Added 'defragsvc' service conflict known issue to README.MD for Disk - Fixes #172

[PlagueHO]

Pull Request (PR) description

This PR Documents the Disk known issue when the 'defragsvc' is started.

I didn't add tests because in my experimentation, this issue does not always 100% happen (it seems to depend on the disk and whether the service is doing work at the time).

This Pull Request (PR) fixes the following issues

• Fixes #172

Task list

• [x] 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 in the resource folder.
• [ ] Resource parameter descriptions added/updated in 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.

@johlju - would you mind reviewing when you get a chance?

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This change is 

[codecov-io]

Codecov Report

Merging #173 into dev will not change coverage. The diff coverage is n/a.

@@        Coverage Diff         @@
##           dev   #173   +/-   ##
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  Coverage   94%    94%           
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  Files        6      6           
  Lines      797    797           
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  Hits       756    756           
  Misses      41     41

[PlagueHO]

Thanks @johlju !!!!