Update ML2 README file for havana
Update ML2 README file for havana

Closes-Bug: 1235308
Change-Id: I684581c00ff28bc9cdb36034a9a970275b0a0090
(cherry picked from commit 2d7e2756271fff6413a572e11f9248465f23f1bb)

kaiweifan/neutron,kaiweifan/neutron,rickerc/neutron_audit,kaiweifan/neutron,rickerc/neutron_audit,rickerc/neutron_audit