Updated isWritable

[Dashboy1998]

Context

• Addressing isWritable check requires that the root directory be deletable ("/palworld is not writable") #358

Choices

• Since [ -w path ] won't work if a directory is writable but not delete-able we check if it is a directory and if so then try to create a temporary file.

Test instructions

1. Start normally. If this works then isWritable works for files and directories that are writable.
2. Verify the function still works for files that are not writable: chmod 444 palworld/Pal/Saved/Config/LinuxServer/PalWorldSettings.ini
3. Verify the function still works for directories that are writable and delete-able: chmod 444 palworld/Pal/Saved/Config/LinuxServer/
4. Verify the function works for directories that are writable but not delete-able

Checklist before requesting a review

• I have performed a self-review of my code
• I've added documentation about this change to the README.
• I've not introduced breaking changes.

[Dashboy1998]

@acmcarther can you test if this resolves your issue? I am unable to test as I do not have an NFS.