fix: typo in USER_GUIDE.md (#1036)

## Summary

Just fixed a typo `Xtink` -> `Xteink`

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**< NO >**_

USER_GUIDE.md

@@ -28,7 +28,7 @@ Welcome to the **CrossPoint** firmware. This guide outlines the hardware control
 
 ## 1. Hardware Overview
 
-The device utilises the standard buttons on the Xtink X4 (in the same layout as the manufacturer firmware, by default):
+The device utilises the standard buttons on the Xteink X4 (in the same layout as the manufacturer firmware, by default):
 
 ### Button Layout
 | Location        | Buttons                                              |