Umineko: No EnableSteamSync.bat equivalent on linux/mac

On the Steam forums, a Mac user asked how to run the `EnableSteamSync.bat` script.

Currently, the only way to enable steam sync on mac or linux is to manually create a linked folder (make a link with `ln` which points `saves` to the `mysav` folder).

I think making a shell script which calls `ln -s mysav saves` (with added checks if the 'saves' folder already exists, as in the current EnableSteamSync batch file) would be enough on linux/mac to get this to work.

The documentation should also be updated to state the OS specific differences. Currently it doesn't say that the `EnableSteamSync.bat` is windows specific.

查看现有的 EnableSteamSync.bat 文件，了解其检查 'saves' 文件夹是否存在的逻辑。创建一个使用 ln -s mysav saves 并具有类似检查的 shell 脚本（可能命名为 EnableSteamSync.sh）。更新文档以提及操作系统特定的差异，说明 .bat 文件仅适用于 Windows，而 .sh 脚本适用于 Linux/Mac。通过在 Linux/Mac 环境中运行脚本来测试，确保它能正确创建符号链接。

由索引模型根据 Issue 内容生成。