Fix manual init with auto performance for RN and iOS (#5600)

Co-authored-by: Isabel <[email protected]>

Author: 2 people

src/platforms/react-native/manual-setup/native-init.mdx

@@ -25,6 +25,11 @@ Do not use `autoInitializeNativeSdk` to disable the native layer, instead use [e
 
 Next, initialize the native SDKs for Android, which is documented below, or for iOS by following the [configuration guide to initialize the Sentry Cocoa SDK](/platforms/apple/guides/ios/#configure). Note that you do not need to install the native SDKs as they are already packaged with the React Native SDK.
 
+## iOS Configuration
+
+To enable App Start Instrumentation and Slow and Frozen Frames on iOS when initializing the Sentry Cocoa SDK manually,
+you have to [configure the sample rate](/platforms/apple/performance/#configure-the-sample-rate/).
+
 ## Android Configuration
 
 <Note>