doc: ls: put option description on separate line to option

doc: ls: put option description on separate line to option

* src/ls.c (usage): This is less constrained when writing comments,
and more consistent in output alignment.  There is less delineation
between options and descripts, but given options are highlighted
by default now, this is a more appropriate format to use.
Note consistently showing description on the line following the option,
avoids any issue with the user needing to visually line up
the option with a description far to the right.
Note this format more closely aligns with that used in man pages.