Add 1.3.20 to version history (#8927) (#8947)

_about/version-history.md

@@ -35,6 +35,7 @@ OpenSearch version | Release highlights | Release date
 [2.0.1](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-2.0.1.md) | Includes bug fixes and maintenance updates for Alerting and Anomaly Detection. | 16 June 2022
 [2.0.0](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-2.0.0.md) | Includes document-level monitors for alerting, OpenSearch Notifications plugins, and Geo Map Tiles in OpenSearch Dashboards. Also adds support for Lucene 9 and bug fixes for all OpenSearch plugins. For a full list of release highlights, see the Release Notes. | 26 May 2022
 [2.0.0-rc1](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-2.0.0-rc1.md) | The Release Candidate for 2.0.0. This version allows you to preview the upcoming 2.0.0 release before the GA release. The preview release adds document-level alerting, support for Lucene 9, and the ability to use term lookup queries in document level security. | 03 May 2022
+[1.3.20](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-1.3.20.md) | Includes enhancements to Anomaly Detection Dashboards, bug fixes for Alerting and Dashboards Reports, and maintenance updates for several OpenSearch components. | 11 December 2024
 [1.3.19](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-1.3.19.md) | Includes bug fixes and maintenance updates for OpenSearch security, OpenSearch security Dashboards, and anomaly detection. | 27 August 2024
 [1.3.18](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-1.3.18.md) | Includes maintenance updates for OpenSearch security. | 16 July 2024
 [1.3.17](https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-1.3.17.md) | Includes maintenance updates for OpenSearch security and OpenSearch Dashboards security. | 06 June 2024