docs: update Node.js version requirement in README

[lumirlumir]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

In this PR, I've updated the Node.js version requirement in README.md.

Based on the CHANGELOG and the engines.node field in package.json, it looks like Node.js 20 is the supported version.

eslint-transforms/CHANGELOG.md

Line 8 in 6e46bf6

* Upgrade dependencies; set Node.js to 20 ([#26](https://github.com/eslint/eslint-transforms/issues/26))

eslint-transforms/package.json

Lines 8 to 10 in 6e46bf6

	"engines": {
	"node": ">=20"
	},

What changes did you make? (Give an overview)

In this PR, I've updated the Node.js version requirement in README.md.

Related Issues

N/A

Is there anything you'd like reviewers to focus on?

I've also corrected some formatting issues throughout the codebase.

Since .editorconfig specifies an indent size of 4, I've updated the code to match.

eslint-transforms/.editorconfig

Line 5 in 6e46bf6

indent_size = 4

[mdjermanovic]

LGTM, thanks!