Update ReleaseNotes.md

Author: keveleigh

Documentation/ReleaseNotes.md

@@ -11,6 +11,12 @@
 
 ## What's new
 
+### Fixes an issue with OpenXR via UPM
+
+Fixes an issue where the OpenXR providers weren't added to the link.xml by default, causing new projects to fail to run on-device when using OpenXR and MRTK via Unity's Package Manager. Existing projects that are upgraded will still need this added manually.
+
+## What was new in 2.5.3
+
 ### Fixes a regression with Oculus introduced in 2.5.2
 
 2.5.2 introduced [a build issue when integrating the Oculus SDK](https://github.com/microsoft/MixedRealityToolkit-Unity/issues/9083). This release reverts that issue.
@@ -38,7 +44,6 @@ Support for MSBuild for Unity has been removed as of the 2.5.2 release, to align
 
 There's currently a known issue with Holographic Remoting and OpenXR, where hand joints aren't consistently available.
 Additionally, the eye tracking sample scenes aren't currently compatible, though eye tracking *does* work.
-Lastly, there's an additional issue where some OpenXR APIs return DllNotFound exceptions if they're called in the editor before an XR session is established.
 
 ### Some Mixed Reality Toolkit Standard Shader features require the Foundation package