docs: clarify $inspect.trace docs (#15858)

* docs: clarify `$inspect.trace` docs

* Update 07-$inspect.md

* Update documentation/docs/02-runes/07-$inspect.md

---------

Co-authored-by: Rich Harris <[email protected]>

Author: benmccann

documentation/docs/02-runes/07-$inspect.md

@@ -52,6 +52,7 @@ This rune, added in 5.14, causes the surrounding function to be _traced_ in deve
 	import { doSomeWork } from './elsewhere';
 
 	$effect(() => {
+		+++// $inspect.trace must be the first statement of a function body+++
 		+++$inspect.trace();+++
 		doSomeWork();
 	});