scripts: Add hook calllable series-push-hook script

Running checkpatch in pre-commit hook could be a constraint
for day to day work. Though, running it before pushing to
zephyr repo is highly recommended.
Add a  series push script callable from pre-push hook.
Document how to use it in contribute section.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
3 files changed