Update Mouse.yaml (#1113)

This adds extra information on image compatibility requirements for
mouse icons.

## Changes

Notes that the image size is required to be smaller than 256x256 for a
mouse icon image.

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---

### AI Summary

- Adds a note in `Mouse.yaml` specifying mouse icon images must not
exceed 256 pixels on any axis for compatibility.

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---------

Author: ProtoValence

content/en-us/reference/engine/classes/Mouse.yaml

@@ -142,6 +142,7 @@ properties:
       cursors:
 
       - The dimensions of the image used determines the size of the cursor.
+      - The dimensions of the image should not exceed 256 pixels on any axis.
       - The **center** of the image is where mouse inputs are issued.
       - The default mouse image is 64x64 pixels, with the mouse taking up 17x24
         pixels of space.