Note to be added for openvswitch-datapath-dkms

This patch adds a note for the openvswitch-datapath-dkms
installation on Ubuntu 14.04.

Change-Id: Idb41a1b6d1a69453ea6c7511721d0e6bdd05886a
Partial-bug: 1371042
Merge "Note to be added for openvswitch-datapath-dkms"