The README documentation shows an example configuration that includes environment variable syntax: README.md:155

However, the current implementation doesn't actually support environment variable expansion. config.rs:24-26

The download_dir field is defined as a plain String type and the configuration loading process directly deserializes the TOML content without any variable substitution: config.rs:107-113

Expected Behavior:
Users should be able to use environment variables like $STU_ROOT_DIR/Downloads in their config.toml file and have them properly expanded.

Actual Behavior:
The literal string $STU_ROOT_DIR/Downloads is used as the directory path, potentially creating a directory named $STU_ROOT_DIR instead of expanding the variable.