Issue in /src/pages/guides/creating-python-plugin.md

I was going over the "Creating a Python plugin" tutorial, and had issues running the custom_import.py plugin code. It seems that PySide 2 is not supported in the most recent version of Substance Painter.

Is the following more appropriate? While I still had errors after making this change, at least it loaded the plugin.

from PySide6 import QtWidgets
from PySide6.QtGui import QAction

从 src/pages/guides/creating-python-plugin.md 开始，结合报告中的 PySide2 和 PySide6 imports 检查 custom_import.py 示例。确认当前 Substance Painter 版本支持哪种 import 形式，然后更新教程，使示例能够在不出现报告中的 import 问题的情况下加载。

由索引模型根据 Issue 内容生成。