doc: announce igb_uio move to an external repository

doc: announce igb_uio move to an external repository

Based on the tech board meeting held on 2019-11-06,
It's been decided to move igb_uio kernel module to a new repository
hosted by dpdk.org in v20.11 release.

http://mails.dpdk.org/archives/dev/2019-November/151763.html

Adding the deprecation notice for the same in advance.

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: David Marchand <david.marchand@redhat.com>