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.

查看現有的 EnableSteamSync.bat 檔案，了解其檢查 'saves' 資料夾是否存在的邏輯。建立一個使用 ln -s mysav saves 並具有類似檢查的 shell 指令碼（可能命名為 EnableSteamSync.sh）。更新文件以提及作業系統特定的差異，說明 .bat 檔案僅適用於 Windows，而 .sh 指令碼適用於 Linux/Mac。透過在 Linux/Mac 環境中執行指令碼來測試，確保它能正確建立符號連結。

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