Explicitly set manpage section numbers

rst2man produces a blank section number in the generated man page's .TH
line, which confuses some tools. (E.g., Debian's dh_installman
interprets the date as the section number.) Explicitly set the manual
section in the RST source.

Signed-off-by: Robert S. Edmonds <edmonds@debian.org>
Signed-off-by: Konstantin Ryabitsev <mricon@kernel.org>