[Bug-cpio] mention to try --extract-over-symlinks

[積丹尼 Dan Jacobson]

$ zcat /var/tmp/cfBAK.27.gz|cpio -idvm /cf/updates/...
cpio: Can't write over symlinks: /cf/updates/...

Fine, but also say
"Try --extract-over-symlinks ."
Else the user gives up.
cpio (GNU cpio) 2.12