README updates
README updates

- correct links to dataplane driver files
- better explanations on bagpipe-rest-attach examples

stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,murat1985/bagpipe-bgp,openstack/networking-bagpipe,murat1985/bagpipe-bgp,openstack/networking-bagpipe-l2,openstack/networking-bagpipe-l2,stackforge/networking-bagpipe-l2