Update mixed-reality-add-pins-3d-model.md

Updated to include coordinate system info which is needed to correctly set pin coordinates

Author: rarattay

powerapps-docs/maker/canvas-apps/mixed-reality-add-pins-3d-model.md

@@ -67,6 +67,9 @@ Y dimension of the pin | PinsY
 Z dimension (depth) of the pin | PinsZ
 
 
+> [!IMPORTANT]
+> The mixed reality controls use a left-handed coordinate system.
+
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