Add example for Prettier ESM config (#263)

* Add example for Prettier ESM config

Thought this might be useful for folks since we are in a shift towards an ESM config future.

* Update README.md

---------

Co-authored-by: Adam Wathan <adam.wathan@gmail.com>

README.md

@@ -10,12 +10,11 @@ To get started, install `prettier-plugin-tailwindcss` as a dev-dependency:
 npm install -D prettier prettier-plugin-tailwindcss
 ```
 
-Then add the plugin to your [Prettier config](https://prettier.io/docs/en/configuration.html):
+Then add the plugin to your [Prettier configuration](https://prettier.io/docs/en/configuration.html):
 
-```js
-// prettier.config.js
-module.exports = {
-  plugins: ['prettier-plugin-tailwindcss'],
+```json
+{
+  "plugins": ["prettier-plugin-tailwindcss"]
 }
 ```