docs(apple, android): Add standalone app start tracing to tracing pages

docs/platforms/android/tracing/index.mdx

@@ -35,6 +35,44 @@ Test out tracing by starting and finishing a transaction, which you _must_ do so
 
 While you're testing, set <PlatformIdentifier name="traces-sample-rate" /> to `1.0`, as that ensures that every transaction will be sent to Sentry. Once testing is complete, you may want to set a lower <PlatformIdentifier name="traces-sample-rate" /> value, or switch to using <PlatformIdentifier name="traces-sampler" /> to selectively sample and filter your transactions, based on contextual data.
 
+## Standalone App Start Tracing
+
+<Alert level="info">
+
+This feature is experimental.
+
+</Alert>
+
+By default, app start data is attached as spans to the first transaction in your app. Standalone app start tracing sends app start data as its own separate transaction instead. This gives you more accurate app start measurements, since they aren't dependent on another transaction being started.
+
+To enable standalone app start tracing, add the following to your `AndroidManifest.xml`:
+
+```xml {filename:AndroidManifest.xml}
+<application>
+  <meta-data android:name="io.sentry.standalone-app-start-tracing.enable" android:value="true" />
+</application>
+```
+
+Or, configure it manually in code:
+
+```java
+import io.sentry.android.core.SentryAndroid;
+
+SentryAndroid.init(this, options -> {
+    options.setEnableStandaloneAppStartTracing(true);
+});
+```
+
+```kotlin
+import io.sentry.android.core.SentryAndroid
+
+SentryAndroid.init(this) { options ->
+    options.isEnableStandaloneAppStartTracing = true
+}
+```
+
+For more details on app start instrumentation, see <PlatformLink to="/tracing/instrumentation/automatic-instrumentation/#app-start-instrumentation">App Start Instrumentation</PlatformLink>.
+
 ## Next Steps
 
 <PageGrid />

docs/platforms/apple/common/tracing/index.mdx

@@ -31,6 +31,32 @@ Test out tracing by starting and finishing a transaction, which you _must_ do so
 
 While you're testing, set <PlatformIdentifier name="traces-sample-rate" /> to `1.0`, as that ensures that every transaction will be sent to Sentry. Once testing is complete, you may want to set a lower <PlatformIdentifier name="traces-sample-rate" /> value, or switch to using <PlatformIdentifier name="traces-sampler" /> to selectively sample and filter your transactions, based on contextual data.
 
+## Standalone App Start Tracing
+
+<Alert level="info">
+
+This feature is experimental.
+
+</Alert>
+
+By default, app start data is attached as spans to the first transaction in your app. Standalone app start tracing sends app start data as its own separate transaction instead. This gives you more accurate app start measurements, since they aren't dependent on another transaction being started.
+
+To enable standalone app start tracing, add the following to your SDK configuration:
+
+```swift
+SentrySDK.start { options in
+    options.experimental.enableStandaloneAppStartTracing = true
+}
+```
+
+```objc
+[SentrySDK startWithConfigureOptions:^(SentryOptions *options) {
+    options.experimental.enableStandaloneAppStartTracing = YES;
+}];
+```
+
+For more details on app start instrumentation, see <PlatformLink to="/tracing/instrumentation/automatic-instrumentation/#app-start-tracing">App Start Tracing</PlatformLink>.
+
 ## Next Steps
 
 <PageGrid />