DOC Add changelog note about SQLUpdate supporting JOIN (#481)

en/08_Changelogs/5.3.0.md

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+---
+title: 5.3.0 (unreleased)
+---
+
+# 5.3.0 (unreleased)
+
+## Overview
+
+- [Features and enhancements](#features-and-enhancements)
+  - [Support for `JOIN` in SQL `UPDATE`](#sql-update-join)
+- [Bug fixes](#bug-fixes)
+
+## Features and enhancements
+
+### Support for `JOIN` in SQL `UPDATE` {#sql-update-join}
+
+The [`SQLUpdate`](api:SilverStripe\ORM\Queries\SQLUpdate) class now supports all of the same `JOIN` operations (using the same methods) that [`SQLSelect`](api:SilverStripe\ORM\Queries\SQLSelect) does.
+
+This is particularly helpful if you need to update columns in one table to match values from another table.
+
+## Bug fixes
+
+This release includes a number of bug fixes to improve a broad range of areas. Check the change logs for full details of these fixes split by module. Thank you to the community members that helped contribute these fixes as part of the release!
+
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