perf annotate: Document --show-total-period option

perf annotate: Document --show-total-period option

When the --show-total-period option was introduced we forgot to add an
entry in the man page, fix it.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Martin Liška <mliska@suse.cz>
Fixes: 0c4a5bcea460 ("perf annotate: Display total number of samples with --show-total-period")
Link: http://lkml.kernel.org/r/1503046013-5555-1-git-send-email-treeze.taeung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>