Add postPublish hooks removal to sentry-expo migration guide

Author: krystofwoldrich

docs/platforms/react-native/migration/sentry-expo.mdx

@@ -22,7 +22,11 @@ yarn remove sentry-expo
 pnpm remove sentry-expo
 ```
 
-### Install `@sentry/react-native`
+### Remove `sentry-expo/upload-sourcemaps` from `postPublish` hooks
+
+Remove the Sentry Source Maps Upload hook from your Expo Application configuration, `expo.hooks.postPublish`. The new methods of uploading source maps are described in the [new Expo guide](/platforms/react-native/manual-setup/expo/), the last step of this migration at the bottom of this page.
+
+## Install `@sentry/react-native`
 
 Install the `@sentry/react-native` package: