posts: email-workflow-for-champions: crontab typo

The crontab entry incorrectly referenced the mail.print script.  The
correct script is mail.cron.

Reported-by: Sebastian Capella <sebastian.capella@linaro.org>
Signed-off-by: Michael Turquette <mturquette@deferred.io>
posts: email-workflow-for-champions: mention w3m

Reported-by: Sebastian Capella <sebastian.capella@linaro.org>
Signed-off-by: Michael Turquette <mturquette@deferred.io>
posts: email-workflow-for-champions: move screencast to the top

Signed-off-by: Michael Turquette <mturquette@deferred.io>