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/tutorials/pattern-design/part3/expand/readme.mdx

@@ -0,0 +1,53 @@
+---
+title: Saving space (and trees) with exand
+order: 40
+---
+
+There is one more way we like to save space (and trees): The `expand` setting.
+
+The `expand` setting (which is true by default) indicates that user wants pattern
+parts to be fully expanded.
+
+It's common to reduce the amount of space required by reducing simple shapes like
+rectangles to a description or cut things on the fold.
+
+The `exand` setting gives the user control over this, at least insofar the designer
+supports it. It's not relevant to our bib, but it's good to know it's there.
+
+Here is an example snippets from [Aaron's arm binding](https://github.com/freesewing/freesewing/blob/develop/designs/aaron/src/arm-binding.mjs#L24):
+
+```mjs
+const w = store.get('bindingWidth')
+const l = store.get('armBindingLength')
+
+if (expand) {
+  store.flag.preset('expandIsOn')
+} else {
+  // Expand is off, do not draw the part but flag this to the user
+  store.flag.note({
+    msg: `aaron:cutArmBinding`,
+    replace: {
+      width: units(w),
+      length: units(l),
+    },
+    suggest: {
+      text: 'flag:show',
+      icon: 'expand',
+      update: {
+        settings: ['expand', 1],
+      },
+    },
+  })
+  // Also hint about expand
+  store.flag.preset('expand')
+
+  return part.hide()
+}
+```
+
+There's some stuff going on here that we'll learn next, but essentially if
+`expand` is falsy, the part will hide itself with `part.hide()` and so it won't
+be included on the pattern.
+
+However, to avoid misunderstandings we want to inform the user about this.
+That's what all those `store.flag` lines are about. We'll learn about then next.