Add references to the gitworkflows(7) manpage added in f948dd8
(Documentation: add manpage about workflows, 2008-10-19) to both
gittutorial(1) and git(1), so that new users might actually discover
and read it.
Noticed by Randal L. Schwartz.
Signed-off-by: Thomas Rast <trast@student.ethz.ch> Signed-off-by: Junio C Hamano <gitster@pobox.com>