docs: Add link to google's update testing tool in migration guide and improve host permission docs

docs/get-started/migrate-to-wxt.md

@@ -25,7 +25,7 @@ In general, you'll need to:
 &ensp;<input type="checkbox" /> Convert custom import syntax to be compatible with Vite<br />
 &ensp;<input type="checkbox" /> Add a default export to JS entrypoints<br />
 &ensp;<input type="checkbox" /> Use the `browser` global instead of `chrome`<br />
-&ensp;<input type="checkbox" /> Compare final `manifest.json` files, making sure permissions and host permissions are unchanged<br />
+&ensp;<input type="checkbox" /> Compare final `manifest.json` files, making sure permissions and host permissions are unchanged. Use [Google's update testing tool](https://github.com/GoogleChromeLabs/extension-update-testing-tool) if your extension is already live on the Chrome Web Store<br />
 &ensp;<input type="checkbox" /> Extension output by `wxt build` works the same way as before the migration<br />
 
 Every project is different, so there's no one-solution-fits-all to migrating your project. Just make sure `wxt dev` runs, `wxt build` results in a working extension, and the list of permissions in the `manifest.json` hasn't changed. If all that looks good, you've finished migrating your extension!

docs/guide/key-concepts/manifest.md

@@ -147,6 +147,31 @@ export default defineConfig({
 });
 ```
 
+### Host Permissions
+
+[Host Permissions](https://developer.chrome.com/docs/extensions/develop/concepts/declare-permissions#host-permissions) must be listed in the manifest config.
+
+```ts
+export default defineConfig({
+  manifest: {
+    host_permissions: ['*://*.google.com/*'],
+  },
+});
+```
+
+:::warning
+If you use host permissions and target both MV2 and MV3, make sure to only include the required host permissions for each version:
+
+```ts
+export default defineConfig({
+  manifest: ({ manifestVersion }) => ({
+    host_permissions: manifestVersion === 2 ? [...] : [...],
+  }),
+});
+```
+
+:::
+
 ## Localization
 
 Similar to the icon, the [`_locales` directory](https://developer.chrome.com/docs/extensions/reference/i18n/) should be placed inside the the WXT's [`public` directory](/guide/directory-structure/public/).