docs: add note for svelte v5 (#499)

Author: ota-meshi

README.md

@@ -3,6 +3,8 @@
 [Svelte] parser for [ESLint].  
 You can check it on [Online DEMO](https://sveltejs.github.io/svelte-eslint-parser/playground).
 
+***Note that this parser has experimental support for Svelte v5, but may break with new versions of Svelte v5.***
+
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