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/hooks/postinit/readme.mdx

@@ -0,0 +1,23 @@
+---
+title: postInit
+---
+
+The `postInit` lifecycle hook runs just after a pattern is initialized.
+
+## Signature
+
+```js
+null hook(Pattern pattern)
+```
+
+## Example
+
+```js
+pattern.on('postInit', pattern => {
+  // Mutate the pattern object here
+}
+```
+
+## Notes
+
+The `postInit` hook is rarely used, but it's there if you need it.