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/api/design/readme.mdx

@@ -0,0 +1,77 @@
+---
+title: Design 
+---
+
+The `Design` named export in FreeSewing's core library is a constructor that
+creates new pattern designs.
+
+## Signature
+
+```js
+Pattern Design({
+  array parts,
+  object data
+})
+```
+
+## Example
+
+```js
+const Sorcha = new Design({ 
+  // design configuration here
+})
+```
+
+This constructor creates a new pattern design.
+It takes a single argument, an object holding the design's configuration.
+
+## Design configuration
+
+Since a design's configuration is managed at the part level,
+the Design configuration object only requires a `parts` property that should
+hold an array of parts to include in the Design.
+
+```js
+const Sorcha = new Design({ 
+  parts: [ front, back, sleeve ],
+})
+```
+
+:::tipA Design in FreeSewing is little more than a container for various Parts:::
+
+Optionally, you can also pass it a `data` attribute
+to hold any custom data you'd like to add to your Design.
+
+Any `data` you add to the Design constructor will be added
+to [the Store](/reference/api/store).
+
+```js
+const Sorcha = new Design({ 
+  parts: [ front, back, sleeve ],
+  data: {
+    version: 3,
+    price: 12,
+    currency: 'euro'
+  }
+})
+```
+
+## Notes
+
+
+The Design constructor is a _super-constructor_. 
+It will return a constructor method that will a pattern based on your design.
+
+## Properties
+
+In addition to the returned constructor method, an instantiated Design object
+also provides the following properties:
+
+### Design.designConfig
+
+This holds the design configuration as passed to the Design constructor.
+
+### Design.patternConfig
+
+Holds the resolved pattern configuration based on the configuration passed to the Design constructor.
+