Updates the stop.md doc to mention that the stop signal can be changed, either with the Dockerfile or via `docker run --stop-signal`. This is a real gotcha if you're not familiar with this feature and build a container that extends a container that uses `STOPSIGNAL`.
Signed-off-by: Christopher Vermilion <christopher.vermilion@gmail.com>
(cherry picked from commit 41d169d211)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
1ff45aac40