Does not work on Arch linux

I am importing using `use systemctl::*;` and running the following code:
```Rust
let services = list_units(None, None).unwrap();
println!("Services: {:?}", services);
```
and I get
`Services: []` no matter what I do.


I validated that `systemctl` is in `/usr/bin/systemctl` and when I run the actual commands locally I do not have any problems.  Am I missing something obvious here?