support: trivial fixes (typos and minor rewording) in gen-manual-lists.py

[Thomas: added Thomas DS Acked-by, given at
http://patchwork.ozlabs.org/patch/284719/

, and made the additional
typo fixes suggested by Thomas DS.]

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>