criu --help: rephrase --pidfile description

... to fit in a single line.
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

crtools.c

@@ -396,8 +396,7 @@ usage:
 "  -s|--leave-stopped    leave tasks in stopped state after checkpoint\n"
 "  -R|--leave-running    leave tasks in running state after checkpoint\n"
 "  -D|--images-dir DIR   directory for image files\n"
-"     --pidfile FILE     write a pid of a root task, service or page-server\n"
-"                        to this file\n"
+"     --pidfile FILE     write root task, service or page-server pid to FILE\n"
 "  -W|--work-dir DIR     directory to cd and write logs/pidfiles/stats to\n"
 "                        if not specified, the --images-dir is used\n"
 "\n"