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/measurements/readme.mdx

@@ -0,0 +1,49 @@
+---
+title: plugin-measurements
+---
+
+Published as [@freesewing/plugin-measurements][1], this plugin will
+provide a number of extra measurements to your design insofar as
+they can be deduced from the measurements that are provided.
+
+It will add the following measurements:
+
+- `seatFront` (if both `seat` and `seatBack` are provided)
+- `seatBackArc` (if both `seat` and `seatBack` are provided)
+- `seatFrontArc` (if both `seat` and `seatBack` are provided)
+- `waistFront` (if both `waist` and `waistBack` are provided)
+- `waistBackArc` (if both `waist` and `waistBack` are provided)
+- `waistFrontArc` (if both `waist` and `waistBack` are provided)
+- `crossSeamBack` (if both `crossSeam` and `crossSeamFront` are provided)
+
+:::note RELATED
+For more information about these extra measurements, please see
+[Measurements from `plugin-measurements`](/reference/measurements#measurements-from-plugin-measurements)
+:::
+
+## Installation
+
+```sh
+npm install @freesewing/plugin-measurements
+```
+
+## 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 { measurementsPlugin } from '@freesewing/plugin-measurements'
+// or
+import { pluginMeasurements } from '@freesewing/plugin-measurements'
+```
+
+## Notes
+
+This plugin is part of the [core-plugins bundle](/reference/plugins/core),
+so there is no need to install or import it manually unless you wish to forego
+loading of core plugins yet still want to load this plugin.
+
+[1]: https://www.npmjs.com/package/@freesewing/plugin-measurements