chore: Updating hooks docs for v3

markdown/dev/reference/api/hooks/postlayout/en.md

@@ -0,0 +1,24 @@
+---
+title: postLayout
+---
+
+The `postLayout` lifecycle hook runs just after the pattern layout is
+calculated.
+
+## Signature
+
+```js
+null hook(Pattern pattern)
+```
+
+## Example
+
+```js
+pattern.on('postLayout', pattern => {
+  // Mutate the pattern object here
+}
+```
+
+## Notes
+
+The `postLayout` hook is rarely used, but it's there if you need it.