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/macros/crossbox/readme.mdx

@@ -0,0 +1,57 @@
+---
+title: crossBox
+---
+
+The `crossbox` macro is used to mark a feature on a sewing pattern 
+to attach and reinforce an attachment between two pieces. 
+This is regularly done by sewing along the outside of the pieces 
+that needs to be joined, and then sewing along the diagonals too.
+
+It is provided by [plugin-annotations](/reference/plugins/annotations), which is
+part of [core-plugins](/reference/plugins/core) (so it is available by default).
+
+## Signature
+
+```js
+macro('crossbox', {
+  String id='crossbox',
+  Point topLeft,
+  Point bottomRight,
+  String text,
+  Boolean force = false,
+})
+```
+
+## Example
+
+<Example caption="An example of the crossbox macro">
+```js
+({ Point, points, Path, paths, macro, part }) => {
+  points.tl = new Point(5,5)
+  points.br = new Point(45,25)
+
+  macro('crossbox', {
+    topLeft: new Point(5, 5),
+    bottomRight: new Point(45, 25),
+    text: 'Attach here',
+  })
+
+  return part
+}
+```
+</Example>
+
+## Configuration
+
+| Property        | Default  | Type                | Description |
+|----------------:|----------|---------------------|-------------|
+| `bottomRight`   |          | [Point](/reference/api/point) | The bottom right point of the crossbox |
+| `topLeft`       |          | [Point](/reference/api/point) | The top left point of the crossbox |
+| `id`            | `crossbox` | `string` | The ID of this macro instance |
+| `text`          |          | String   | Optional text to go in the center of the crossbox |
+| `force`         | `false`    | `boolean`  | Set this to `true` to display the macro output even when `complete` is `false` |
+
+## Notes
+
+This macro takes the `complete` setting into account and won't output anything when both complete and `force` are `false`.
+