Added missing ' .' in the command 'git add' present in README.md

[ghost]

Added missing ' .' in the command 'git add' present in README.md

Issue Number

fixes #

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Test plan (OPTIONAL)

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Checklist

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] All new and existing tests passed.
• [ ] The title of my pull request is a short description of the requested changes.