chore: doc fix (#15651)

Author: Rich-Harris

documentation/docs/98-reference/.generated/client-errors.md

@@ -151,6 +151,8 @@ This error occurs when state is updated while evaluating a `$derived`. You might
 This is forbidden because it introduces instability: if `<p>{count} is even: {even}</p>` is updated before `odd` is recalculated, `even` will be stale. In most cases the solution is to make everything derived:
 
 ```js
+let count = 0;
+// ---cut---
 let even = $derived(count % 2 === 0);
 let odd = $derived(!even);
 ```

packages/svelte/messages/client-errors/errors.md

@@ -107,6 +107,8 @@ This error occurs when state is updated while evaluating a `$derived`. You might
 This is forbidden because it introduces instability: if `<p>{count} is even: {even}</p>` is updated before `odd` is recalculated, `even` will be stale. In most cases the solution is to make everything derived:
 
 ```js
+let count = 0;
+// ---cut---
 let even = $derived(count % 2 === 0);
 let odd = $derived(!even);
 ```