perf annotate: shorten helpline so it fits in visible space

Additional toggles have pushed the help line out of view on a modestly
sized terminal (120 columns wide). Shorten it to just reminders.

Signed-off-by: David Ahern <dsahern@gmail.com>
Link: http://lkml.kernel.org/r/1336510879-64610-1-git-send-email-dsahern@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>