The --log-pid option was introduced with commit

fc7bedc5
crtools: make to be able to split messages by pid

This option is applicable only for restore. Therefore, move the
documentation from "Common options" to "restore".
Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>