Add opentelemetry-python ASGI integration (#47)

* Add opentelemetry-python ASGI integration

* Update README.md

* Use latest docs version

README.md

@@ -83,6 +83,7 @@ _Packages for monitoring ASGI web applications._
 
 <!-- sort_by:name -->
 
+- [opentelemetry-python](https://opentelemetry-python.readthedocs.io/en/latest/instrumentation/asgi/asgi.html) - ASGI middleware and helpers for collecting application metrics via the (currently alpha) OpenTelemetry standard. Supports HTTP and WebSocket.
 - [Scout APM Starlette](https://docs.scoutapm.com/#starlette) - Scout APM integration with Starlette and Starlette-based frameworks. (Shipped with `scout-apm`.)
 - [Sentry ASGI](https://docs.sentry.io/platforms/python/asgi/) - Sentry integration for ASGI frameworks. (Shipped with `sentry-sdk`.)
 - [timing-asgi](https://github.com/steinnes/timing-asgi) - ASGI middleware to record and emit timing metrics.