Updated release process documentation.
Updated release process documentation.

Added a note about git shortlog, I keep forgetting the command.

Signed-off-by: Jan Safranek <a7f4b96ffdd515ecef00f117294da18555749b0b@redhat.com>

rafalmiel/libcg,rafalmiel/libcg,rafalmiel/libcg,rafalmiel/libcg