criu --help: rectify --ext-unix-sk
criu --help: rectify --ext-unix-sk

* add missing space between option and the argument
* mark argument as optional
* fix English
* obey 80 columns width

Was:
  -x|--ext-unix-skinode,..      allow external unix connections (optionally can be assign socket's inode that allows one-sided dump)

Now:
  -x|--ext-unix-sk [inode,...]
                        allow external unix connections (optional arguments
                        are socketpair inode(s) that allow one-sided dump)

Signed-off-by: Kir Kolyshkin <c0159612b0ef32139322233232df1a0d189c4b9b@openvz.org>
Acked-by: Cyrill Gorcunov <7a1ea01eee6961eb1e372e3508c2670446d086f4@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

eabatalov/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu,eabatalov/criu