chore(instr-express): add semconv to readme (#1907)

* chore(instr-express): add semconv to readme

* use actual attribute field in readme

* specify the semantic-conventions package

---------

Co-authored-by: Marc Pichler <[email protected]>

Author: JamieDanielson

plugins/node/opentelemetry-instrumentation-express/README.md

@@ -142,6 +142,16 @@ const expressInstrumentation = new ExpressInstrumentation({
 });
 ```
 
+## Semantic Conventions
+
+This package uses `@opentelemetry/semantic-conventions` version `1.0+`, which implements Semantic Convention [Version 1.7.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.7.0/semantic_conventions/README.md)
+
+Attributes collected:
+
+| Attribute    | Short Description                  | Notes             |
+| ------------ | ---------------------------------- | ----------------- |
+| `http.route` | The matched route (path template). | Key: `HTTP_ROUTE` |
+
 ## Useful links
 
 - For more information on OpenTelemetry, visit: <https://opentelemetry.io/>