chore: Update README for prettier v3.x

[basselworkforce]

While testing with prettier v3 I found that it is now necessary to add the plugin to the config with npm (when I never had to before) as per:

module.exports = {
    ...
    "plugins": ["@trivago/prettier-plugin-sort-imports"]
}

https://github.com/trivago/prettier-plugin-sort-imports#usage

[lukeapage]

Confirmed - same for me.

I got warnings about unknown config options and at first I thought this was the issue, but it was because the plugin was no longer auto loaded.