Add migration docs

Author: lachlancollins

docs/config.json

@@ -127,6 +127,10 @@
             {
               "label": "SSR & SvelteKit",
               "to": "framework/svelte/ssr"
+            },
+            {
+              "label": "Migrate from v5 to v6",
+              "to": "framework/svelte/migrate-from-v5-to-v6"
             }
           ]
         },

docs/framework/svelte/migrate-from-v5-to-v6.md

@@ -0,0 +1,58 @@
+## Overview
+
+While Svelte v5 has legacy compatibility with the stores syntax from Svelte v3/v4, it has been somewhat buggy and unreliable for this TanStack Query adapter. The `@tanstack/svelte-query` v6 adapter fully migrates to runes syntax.
+
+## Installation
+
+Run `pnpm add @tanstack/svelte-query@latest` (or your package manager's equivalent).
+
+> Note that `@tanstack/svelte-query` v6 depends on `@tanstack/query-core` v5.
+
+## Thunks
+
+Like the Solid adapter, most functions for the Svelte adapter now require options to be provided as a "thunk" (`() => options`) to maintain reactivity.
+
+```diff
+-const query = createQuery({
++const query = createQuery(() => ({
+  queryKey: ['todos'],
+  queryFn: () => fetchTodos(),
+-})
++}))
+```
+
+## Accessing Properties
+
+Given the adapter no longer uses stores, it is no longer necessary to prefix with `$`.
+
+```diff
+-{#if $todos.isSuccess}
++{#if todos.isSuccess}
+  <ul>
+-    {#each $todos.data.items as item}
++    {#each todos.data.items as item}
+      <li>{item}</li>
+    {/each}
+  </ul>
+{/if}
+```
+
+## Disabling Legacy Mode
+
+If your component has any stores, it might not properly switch to runes mode. You can ensure your application is using runes in two ways:
+
+### On a per-file basis
+
+In each `.svelte` file, once you have migrated to runes, add `<svelte:options runes={true} />`. This is better for large applications requiring gradual migration.
+
+### On an project-wide basis
+
+In your `svelte.config.js`, add the following to config:
+
+```json
+  compilerOptions: {
+    runes: true,
+  },
+```
+
+This can be added once you've 100% eradicated stores syntax from your app.

docs/framework/svelte/overview.md

@@ -5,6 +5,8 @@ title: Overview
 
 The `@tanstack/svelte-query` package offers a 1st-class API for using TanStack Query via Svelte.
 
+> Migrating from stores to the runes syntax? See the [migration guide](../migrate-from-v5-to-v6).
+
 ## Example
 
 Include the QueryClientProvider near the root of your project: