bug#370: dired "total used in directory 116 available 1025920"

[jidanni]

Somewhere in Info "38 Dired, the Directory Editor", it should mention
the proprietary secret of how it manages to put
  total used in directory 116 available 1025920
into the buffer, whereas everybody else outside of dired only can get
  total 116
with all the ls flags they can find a-blazing.
Indeed, all dired uses is ls --dired -alo -- /mnt/bla/.
so mention that the bonus information is not something one can get
with plain ls, and must use df...