Improve documentation of @swc/plugin-formatjs

[mimecuvalo]

Hiya, right now there's no documentation for the @swc/plugin-formatjs plugin, it's just a changelog: https://www.npmjs.com/package/@swc/plugin-formatjs

The previous documentation gave an overview of how to use the plugin: https://github.com/formatjs/formatjs/blob/0e240f4716a65db231212ba59b0a1d19f6b57c3e/website/docs/tooling/swc-plugin.md

It would be good to restore that so that people can more easily use it.

[kdy1]

Can you send a PR?