doc: help2man: recognise option description with smaller indent

doc: help2man: recognise option description with smaller indent

* man/help2man: Allow for a smaller indented option description.
This smaller indentation is present in timeout --help output,
so now the line spacing in timeout.1 is more consistent.
Also having the description on a separate line with
a smaller indentation, is a more general way to present
option descriptions (and what the man page formatting uses already).
We'll be changing many utilities, especially with longer multi-line
descriptions to this new format.