fix: update package.json and README to use pnpm instead of npm

[Razzaghnoori]

Since we are using pnpm as the package manager, any attempt to use npm will result in failure.

🔗 Linked issue

fix #178

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/nuxt/hints/@nuxt/hints@179

commit: f98b0ce

[huang-julien]

Thanks !