update comment about source

Author: LadyBluenotes

src/routes/reference/basic-reactivity/create-resource.mdx

@@ -92,8 +92,10 @@ interface ResourceOptions<T, S = unknown> {
 - **Type:** `ResourceSource<S>`
 - **Default:** `undefined`
 
-Reactive data source whose non-nullish and non-false values are passed to the fetcher.
-When the source changes, the fetcher is automatically re-run.
+Reactive data source whose value, when coerced to a boolean, determines whether the fetcher runs. 
+If the value is truthy, it is passed as the first argument to the fetcher. 
+If the value is falsy (including `undefined`, `null`, `false`, `0`, `""`, or `NaN`), the fetcher will not be called. 
+Once the source changes to a truthy value, the fetcher automatically re-runs.
 
 ### `fetcher`