docs: add eslint migration

Author: dummdidumm

documentation/docs/05-misc/04-v4-migration-guide.md

@@ -159,6 +159,10 @@ This makes slot bindings more consistent as the behavior is undefined when for e
 
 The order in which preprocessors are applied has changed. Now, preprocessors are executed in order, and within one group, the order is markup, script, style. Each preprocessor must also have a name. ([#8618](https://github.com/sveltejs/svelte/issues/8618))
 
+## New eslint package
+
+`eslint-plugin-svelte3` is deprecated. It may still work with Svelte 4 but we make no guarantees about that. We recommend switching to our new package [eslint-plugin-svelte](https://github.com/sveltejs/eslint-plugin-svelte). See [this Github post](https://github.com/sveltejs/kit/issues/10242#issuecomment-1610798405) for an instruction how to migrate. Alternatively, you can create a new project using `npm create svelte@latest`, select the eslint (and possibly TypeScript) option and then copy over the related files into your existing project.
+
 ## Other breaking changes
 
 - the `inert` attribute is now applied to outroing elements to make them invisible to assistive technology and prevent interaction. ([#8628](https://github.com/sveltejs/svelte/pull/8628))