docs: fix README install package name

[JSap0914]

Summary

• Fix the README yarn and npm install commands to use the published package name, @nbazille/prettier-plugin-qml.
• Replace the misspelled prettie-plugin-qml references in the install examples.

Fixes #55.

Verification

• git diff --check
• Confirmed package.json declares @nbazille/prettier-plugin-qml as the package name.
• Confirmed open PR duplicate searches returned no matching PR before creation.

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