Disk columns

[gepbird]

Checklist

• I've looked through the documentation and existing open issues for similar feature requests.

Describe the feature request

Similarly to how we can customize processes.column, there could be disks.columns.

I'm trying to create a layout where I allocate a smaller space to the disk widget, but I only see the first 3 column: Disk, Mount and Used. It would be nice if I could change it to Mount, Used% and R/s for example.

[ClementTsang]

Huh, I thought I had added that, but I guess not. Yeah, that should be easy to do.