Add a note that bind:files is readonly (#6099)

site/content/docs/02-template-syntax.md

@@ -585,7 +585,7 @@ Numeric input values are coerced; even though `input.value` is a string as far a
 
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-On `<input>` elements with `type="file"`, you can use `bind:files` to get the [`FileList` of selected files](https://developer.mozilla.org/en-US/docs/Web/API/FileList).
+On `<input>` elements with `type="file"`, you can use `bind:files` to get the [`FileList` of selected files](https://developer.mozilla.org/en-US/docs/Web/API/FileList). It is readonly.
 
 ```sv
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