Non-default Steam folder location

[Zebouski]

Hi there, thank you for this tool I appreciate it I was having trouble setting up this mod manager by hand.

--steam does not work if you have never set up a steam shortcut:

Traceback (most recent call last):
  File "/home/zeb/Modding/BG3 Mod Manager/./linux.py", line 258, in <module>
    main()
  File "/home/zeb/Modding/BG3 Mod Manager/./linux.py", line 246, in main
    add_to_steam()
  File "/home/zeb/Modding/BG3 Mod Manager/./linux.py", line 173, in add_to_steam
    with open(shortcuts_file, 'rb') as f:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/home/zeb/.steam/steam/userdata/75027093/config/shortcuts.vdf'```

Perhaps check for this and inform the user to create a new shortcut in steam, which then fixes this issue.