Docker container throws non-descript "permission denied" error when /app is non-writeable

[garethhumphriesgkc]

When running, I get an error:

thread 'main' panicked at src/config.rs:112:53:
called `Result::unwrap()` on an `Err` value: Os { code: 13, kind: PermissionDenied, message: "Permission denied" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This was caused by /app not being writeable by user 1001

Suggest a more descriptive error message could be displayed in this case.