docs: clarify OTEL_EXPORTER_OTLP_HEADERS automatic support

- Document that SDK automatically reads OTEL_EXPORTER_OTLP_HEADERS
- Add OTEL_EXPORTER_OTLP_TRACES_HEADERS to environment variables list
- Clarify no additional code configuration is required
- Improve Honeycomb example description

Co-authored-by: Ona <no-reply@ona.com>

Author: corneliusludmann

README.md

@@ -610,12 +610,14 @@ export OTEL_EXPORTER_OTLP_ENDPOINT=localhost:4318
 export OTEL_EXPORTER_OTLP_INSECURE=true
 leeway build :my-package
 
-# Production (Honeycomb)
+# Production (Honeycomb with API key)
 export OTEL_EXPORTER_OTLP_ENDPOINT=api.honeycomb.io:443
 export OTEL_EXPORTER_OTLP_HEADERS="x-honeycomb-team=YOUR_API_KEY"
 leeway build :my-package
 ```
 
+The OpenTelemetry SDK automatically reads standard `OTEL_EXPORTER_OTLP_*` environment variables.
+
 **For detailed configuration, examples, and span attributes, see [docs/observability.md](docs/observability.md).**
 
 # Provenance (SLSA) - EXPERIMENTAL

docs/observability.md

@@ -46,9 +46,13 @@ Leeway supports W3C Trace Context propagation, allowing builds to be part of lar
 
 - `OTEL_EXPORTER_OTLP_ENDPOINT`: OTLP endpoint URL (e.g., `localhost:4318` or `api.honeycomb.io:443`)
 - `OTEL_EXPORTER_OTLP_INSECURE`: Disable TLS for OTLP endpoint (`true` or `false`, default: `false`)
+- `OTEL_EXPORTER_OTLP_HEADERS`: HTTP headers for OTLP requests (e.g., `x-honeycomb-team=YOUR_API_KEY`)
+- `OTEL_EXPORTER_OTLP_TRACES_HEADERS`: Trace-specific headers (takes precedence over `OTEL_EXPORTER_OTLP_HEADERS`)
 - `TRACEPARENT`: W3C Trace Context traceparent header (format: `00-{trace-id}-{span-id}-{flags}`)
 - `TRACESTATE`: W3C Trace Context tracestate header (optional)
 
+**Note:** The OpenTelemetry SDK automatically reads `OTEL_EXPORTER_OTLP_HEADERS` and `OTEL_EXPORTER_OTLP_TRACES_HEADERS` from the environment. No additional configuration is required.
+
 ### CLI Flags
 
 - `--otel-endpoint`: OTLP endpoint URL (overrides `OTEL_EXPORTER_OTLP_ENDPOINT`)