t7512-status-help.sh: better advices for git status

t7512-status-help.sh: better advices for git status

The following tests include several cases in which the user needs to
run 'git status' to know his current situation, whether there're
conflicts or he's in rebase/bisect/am/cherry-pick progress.

One of the test is about the set of the advice.statushints config key
to 'false' in .git/config.

Signed-off-by: Lucien Kong <Lucien.Kong@ensimag.imag.fr>
Signed-off-by: Valentin Duperray <Valentin.Duperray@ensimag.imag.fr>
Signed-off-by: Franck Jonas <Franck.Jonas@ensimag.imag.fr>
Signed-off-by: Thomas Nguy <Thomas.Nguy@ensimag.imag.fr>
Signed-off-by: Huynh Khoi Nguyen Nguyen <Huynh-Khoi-Nguyen.Nguyen@ensimag.imag.fr>
Signed-off-by: Matthieu Moy <Matthieu.Moy@grenoble-inp.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>