criu --help: minor cleanups

1. "written in file" -> "written to file"

2. "relative path is relative" -> "path is relative"

3. "each restored processes is written to the FILE.pid file\n" ->
   "log of each restored process is written to a separate FILE.pid file"

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>