pmap: tweak help text, show usage if no params are given

Noticed while auditing nofork/noexec status

function                                             old     new   delta
pmap_main                                             70      80     +10
packed_usage                                       31747   31744      -3

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2 files changed