Update README.md

[johlju]

Pull Request (PR) description

• Add new AppVeyor status badge token

This Pull Request (PR) fixes the following issues

Task list

• Added an entry under the Unreleased section in the CHANGELOG.md.
  Entry should say what was changed, and how that affects users (if applicable).
• Resource documentation added/updated in resource directory README.md.
• 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.

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This change is 

[johlju]

Reviewed 1 of 1 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[codecov-io]

Codecov Report

Merging #449 into dev will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##            dev   #449   +/-   ##
===================================
  Coverage    98%    98%           
===================================
  Files        20     20           
  Lines      2704   2704           
  Branches     10     10           
===================================
  Hits       2651   2651           
  Misses       43     43           
  Partials     10     10