docs(readme): add Braintrust to integrations list (traceloop#2302)

Author: ornellaaltunyan

README.md

@@ -92,6 +92,7 @@ Traceloop.init(disable_batch=True)
 - ✅ [Traceloop](https://www.traceloop.com/docs/openllmetry/integrations/traceloop)
 - ✅ [Axiom](https://www.traceloop.com/docs/openllmetry/integrations/axiom)
 - ✅ [Azure Application Insights](https://www.traceloop.com/docs/openllmetry/integrations/azure)
+- ✅ [Braintrust](https://www.traceloop.com/docs/openllmetry/integrations/braintrust)
 - ✅ [Datadog](https://www.traceloop.com/docs/openllmetry/integrations/datadog)
 - ✅ [Dynatrace](https://www.traceloop.com/docs/openllmetry/integrations/dynatrace)
 - ✅ [Grafana](https://www.traceloop.com/docs/openllmetry/integrations/grafana)