docs: note that docker options require app rebuilds
docs: note that docker options require app rebuilds

Closes #4101

progrium/dokku,claytonbrown/dokku,dokku/dokku,claytonbrown/dokku,progrium/dokku,claytonbrown/dokku,progrium/dokku,claytonbrown/dokku,claytonbrown/dokku,dokku/dokku,progrium/dokku,dokku/dokku,dokku/dokku,dokku/dokku,claytonbrown/dokku,dokku/dokku,dokku/dokku,progrium/dokku,claytonbrown/dokku,progrium/dokku,progrium/dokku,progrium/dokku,claytonbrown/dokku,dokku/dokku