I keep seeing people miss the --context option in the "west flash
--help" output.
This option is very important for understanding the runner-specific
options and state, and missing it means people get confused about what
west flash, debug, etc. can do and are doing.
Try to avoid this problem by adding a big fat banner about the
omission of runner-specific options in the main help output, and
provide more hints about how to use --context.
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
