Update opentelemetry.md

Updated the OTLP metrics endpoint for OpenTelemetry configuration.

The specification states that the OTEL_EXPORTER_OTLP_ENDPOINT is used as a base URL and that metrics path "/v1/metrics" will be appended.

Signed-off-by: Mark O'Connor <mark@myspotontheweb.com>

Author: myspotontheweb

docs/guides/opentelemetry.md

@@ -27,9 +27,15 @@ OpenTelemetry SDKs and instrumentation libraries can be usually configured via [
 
 ```shell
 export OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
-export OTEL_EXPORTER_OTLP_METRICS_ENDPOINT=http://localhost:9090/api/v1/otlp/v1/metrics
+export OTEL_EXPORTER_OTLP_METRICS_ENDPOINT=http://localhost:9090/api/v1/otlp
 ```
 
+Note:
+
+* The [OpenTelemtry specification](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.50.0/specification/protocol/exporter.md#endpoint-urls-for-otlphttp) states that the  OTEL_EXPORTER_OTLP_METRICS_ENDPOINT env var must be used as a base URL. The signal ```/v1/metrics``` is automatically appended
+* See also: [opentelemetry-python #2443](https://github.com/open-telemetry/opentelemetry-python/issues/2443)
+
+
 Turn off traces and logs:
 
 ```shell