Add release notes for OpenSearch beta1 release (#8)

Signed-off-by: David Cui <[email protected]>

release-notes/opensearch-trace-analytics.release-notes-1.0.0.0-beta1.md

@@ -0,0 +1,10 @@
+## 2021-04-26 Version 1.0.0.0-beta1
+Compatible with OpenSearch 1.0.0-beta1
+
+## OpenSearch Migration
+* Migrate trace analytics to OpenSearch Dashboards ([#1](https://github.com/opensearch-project/trace-analytics/pull/1))
+* Change nav bar to use OpenSearch ([#2](https://github.com/opensearch-project/trace-analytics/pull/2))
+* Add license headers for OpenSearch ([#3](https://github.com/opensearch-project/trace-analytics/pull/3))
+* Change plugin versions to 1.0.0 ([#4](https://github.com/opensearch-project/trace-analytics/pull/4))
+* Rebase commits from opendistro repo ([#5](https://github.com/opensearch-project/trace-analytics/pull/5))
+* Bump Version to Beta1 for OpenSearch Release ([#7](https://github.com/opensearch-project/trace-analytics/pull/7))