chore: Port FreeSewing.dev to docusaurus

The replaces the NextJS site powering FreeSewing.dev with a Docusaurus
setup. It's part of my efforts to simplify FreeSewing's setup so we can
focus on our core value proposition.

sites/dev/docs/reference/plugins/i18n/readme.mdx

@@ -0,0 +1,64 @@
+---
+title: plugin-i18n
+---
+
+Published as [@freesewing/plugin-i18n][1], this plugin facilitates
+translation of your designs by allowing you to provide your own
+language translations.
+
+## Installation
+
+```sh
+npm install @freesewing/plugin-i18n
+```
+
+## Usage
+
+Either [add it as a part plugins](/reference/api/part/config/plugins) in your
+design, or [add it to a pattern instance with
+Pattern.use()](/reference/api/pattern/use).
+
+To import the plugin for use:
+```js
+import { i18nPlugin } from '@freesewing/plugin-i18n'
+// or
+import { pluginI18n } from '@freesewing/plugin-i18n'
+```
+
+## Notes
+
+This plugin provides the mechanism for translation but does not come with
+translations itself. For this, you can use our [i18n
+package](https://www.npmjs.com/package/@freesewing/i18n).
+
+To add your own translations, you will need to pass data to this plugin
+containing translation keys and the translations for them for each language.
+The data should be in the form of an `Object` structured as such:
+
+```js
+{
+  strings:
+    en: {
+      example: "Example",
+      examplePhrase: "An example phrase",
+      anotherTranslationKey: "(English translation for the translation key)",
+      // More translations can follow...
+    },
+    nl: {
+      example: "Voorbeeld",
+      examplePhrase: "Een voorbeeldzin",
+      anotherTranslationKey: "(Dutch translation for the translation key)",
+      // More translations can follow...
+    },
+    es: {
+      example: "Ejemplo",
+      examplePhrase: "Una frase de ejemplo",
+      anotherTranslationKey: "(Spanish translation for the translation key)",
+      // More translations can follow...
+    },
+    // More languages can follow...
+  }
+}
+```
+
+[1]: https://www.npmjs.com/package/@freesewing/plugin-i18n