update readme. fix documentation for syntax highlighting

[kimbaudi]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

import prismjs styles from path to cjs instead of esm.

many people using react-markdown are getting error because of this incorrect line of code. see react-syntax-highlighter/react-syntax-highlighter#230. updating the readme should clear up any confusion.

[ChristianMurphy]

Some additional context, for most ESM related issues with Next https://nextjs.org/blog/next-11-1#es-modules-support is an appropriate solution.
However it doesn't solve this https://codesandbox.io/s/next-syntax-highlight-ymmq3?file=/next.config.js
react-syntax-highlighter is psuedo-esm vercel/next.js#27876 (reply in thread) and https://github.com/react-syntax-highlighter/react-syntax-highlighter/blob/3ead4ba5963ac797093fb872375bf713c1372f9a/package.json#L5-L6

This should be addressed when react-syntax-highlighter upgrades to refractor 4 react-syntax-highlighter/react-syntax-highlighter#420 which is itself ESM https://github.com/wooorm/refractor/releases/tag/4.0.0, and will likely encourage react-syntax-highlighter to also package standard ESM https://nodejs.org/api/esm.html#esm_modules_ecmascript_modules

[kimbaudi]

When I first heard about Next.js supporting ESM from vercel/next.js#9607, I thought I would be able to convert next.config.js from cjs to esm, but unfortunately it has to remain cjs 😢. I hope this is supported in the near future.

[wooorm]

This project itself and all examples use actual ESM, I don’t think this should be added.

[kimbaudi]

ok thats fine. closing this