doc: reformat the paragraph containing the 'cut-line'

doc: reformat the paragraph containing the 'cut-line'

The paragraph that describes the 'scissors' cleanup mode of
'commit' had the 'cut-line' in the middle of a sentence. This
made it possible for the line to get wrapped on smaler windows.
This shouldn't be the case as it makes it hard for the user to
understand the structure of the cut-line.

Reformat the pragraph to make the 'cut-line' stand on a line of
it's own thus distinguishing it from the rest of the paragraph.
This further prevents it from getting wrapped to some extent.

Signed-off-by: Kaartic Sivaraam <kaarticsivaraam91196@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>