feat(native): update sentry-trace header format

Author: JoshuaMoelans

platform-includes/distributed-tracing/custom-instrumentation/native.mdx

@@ -36,7 +36,9 @@ To create a transaction as a continuation of a trace retrieved from an upstream
     sentry_transaction_context_update_from_header(
         tx_ctx,
         "sentry-trace",
-        "atraceid-aspanid-issampled"
+        "41c74c2ea9f2bfb184f86939de5b97aa-399b3e5cc8b83494-1"
     );
 
 ```
+
+The format of the `sentry-trace` header should follow the one defined in [the telemetry docs](https://develop.sentry.dev/sdk/telemetry/traces/#header-sentry-trace). It should consist of a 32 character hexadecimal string for the `traceId`, followed by a 16 character hexadecimal string for the `spanId` and an optional single character for the `sampled` flag.