chore: add minimum node.js versions

[KyleBlankRollins]

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Summary

This PR adds a "Before you begin" section to the docs site's main page (README.md). It includes information about required minimum versions of Node.js.

Because the edits are directly to README.md and none of the auto-generated command documentation, I didn't run npm run docs.

---

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• Open a bug/issue before writing your code 🧑‍💻. This ensures we can discuss the changes and get feedback from everyone that should be involved. If you`re fixing a typo or something that`s on fire 🔥 (e.g. incident related), you can skip this step.
• Read the contribution guidelines 📖. This ensures your code follows our style guide and
  passes our tests.
• Update or add tests (if any source code was changed or added) 🧪
• Update or add documentation (if features were changed or added) 📝
• Make sure the status checks below are successful ✅

A picture of a cute animal (not mandatory, but encouraged)

[github-actions]

📊 Benchmark results

Comparing with a87a9ce

Package size: 363 MB

(no change)

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• T (current commit): 363 MB

[ehmicky]

Thanks @KyleBlankRollins!