Updates README.md in training-guides/labs
Updates README.md in training-guides/labs

Adds details for using the osbash scripts
in labs section for training purpose.

Partial-bug: #1362088

Change-Id: I639432e18c46efbcd851cee188870b10c0822d5a

openstack/training-guides,harrisonfeng/training-guides,harrisonfeng/training-guides,harrisonfeng/training-guides,Nabs007/training-guides,Nabs007/training-guides,Nabs007/training-guides,openstack/training-guides