Add branch management for releases to gitworkflows

Add branch management for releases to gitworkflows

The current man page does a reasonable job at describing branch management
during the development process, but it does not contain any guidance as to
how the branches are affected by releases.

Add a basic introduction to the branch management undertaken during a
git.git release, so that a reader may gain some insight into how the
integration, maintenance, and topic branches are affected during the
release transition, and is thus able to better design the process for their
own project.

Other release activities such as reviews, testing, and creating
distributions are currently out of scope.

Signed-off-by: Nanako Shiraishi <nanako3@lavabit.com>
Acked-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>