[FAQ] Clarify GParted usage instructions

The documentation could mention that gparted can be launched using:

```bash
sudo -E gparted
```

This assumes sudo is installed, which is the case for most systems. I think this is a better solution to be in the FAQ, not everyone has xauth or xhost.

https://github.com/labwc/labwc.github.io/blob/main/src/faq.md?plain=1#L326

