docs: add otel export warning (#99)

Author: jer96

docs/user-guide/observability-evaluation/traces.md

@@ -79,7 +79,8 @@ Strands natively integrates with OpenTelemetry, an industry standard for distrib
 
 ## Enabling Tracing
 
-You can enable tracing either through environment variables or through code:
+!!! warning "To enable OTEL exporting, install Strands Agents with `otel` extra dependencies: `pip install strands-agents[otel]`"
+
 
 ### Environment Variables