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/readme.mdx

@@ -0,0 +1,18 @@
+---
+title: "Part 3: Beyond the basics"
+---
+
+I'm excited about diving into part 3 with you, and I hope that a brief
+overview of what we'll cover will get you excited too:
+
+- Adding seam allowance
+- Dealing with laser cutters
+- Providing paperless patterns
+- Limiting output through expand
+- Facilitating frontend integration
+- How to communicate to the user
+- Testing your designs
+- Supporting translation
+
+If that sounds like something you'd like to learn more about, then let's dive
+right in.