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/howtos/code/shared-dimensions/readme.mdx

@@ -0,0 +1,37 @@
+---
+title: Share dimensions between pattern parts
+---
+
+When you have different pattern parts that look similar -- like the front
+and back of a garment -- you may find that there's a lot of dimensions
+shared between them.
+
+The example below is from Aaron where dimensions are shared between
+the back and front part.
+
+Aaron has a file called `shared.mjs` that looks like this:
+
+```js
+export function dimensions(macro, points, sa) {
+  macro('hd', {
+    from: points.cfHem,
+    to: points.hem,
+    y: points.hem.y + sa * 2.5 + 15
+  })
+  // more dimensions here
+}
+```
+
+In both `front.mjs` and `back.mjs` we use this code to add these shared
+dimensions:
+
+```js
+import { dimensions } from './shared'
+
+// ...
+
+  if (paperless) {
+    dimensions(macro, points, sa)
+    // ... dimensions specific to this part
+  }
+```