Updated REAME.md

[samgrulich]

removed trailing '/' from packer instalation (caused trouble with direct copy, then installation)

Fixes Issue

Changes proposed

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• My code follows the code style of this project.
• My change requires changes to the documentation.
• I have updated the documentation accordingly.
• All new and existing tests passed.
• This PR does not contain plagiarized content.
• The title of my pull request is a short description of the requested changes.

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