Add B3 exporter to alpha release table
@@ -81,6 +81,7 @@ release.
| Tracing SDK | Alpha | September 30 2019 |
| Metrics API | Alpha | September 30 2019 |
| Metrics SDK | Alpha | September 30 2019 |
+| Zipkin Trace Exporter | Alpha | September 30 2019 |
| Jaeger Trace Exporter | Alpha | Unknown |
| Prometheus Metrics Exporter | Alpha | Unknown |
| Context Propagation | Alpha | September 30 2019 |
