Add more usage details in README?

The README states that AWS don't recommend using this SDK, however that's not the case if all you want is X-Ray. Also if using Node 18 with ESM handlers, then there currently is no other option than this SDK due to [this issue](https://github.com/open-telemetry/opentelemetry-js/issues/1946).

https://docs.aws.amazon.com/xray/latest/devguide/xray-instrumenting-your-app.html#xray-instrumenting-choosing

We recommend choosing an X-Ray SDK for instrumenting your application if you need the following:

* A tightly integrated single-vendor solution

* Integration with X-Ray centralized sampling rules, including the ability to configure sampling rules from the X-Ray console and automatically use them across multiple hosts, when using Node.js, Python, Ruby, or .NET