add docs of cpi ng
add docs of cpi ng

mattcui/bosh-softlayer-cpi-release,maximilien/bosh-softlayer-cpi,mattcui/bosh-softlayer-cpi-release,maximilien/bosh-softlayer-cpi,mattcui/bosh-softlayer-cpi-release,mattcui/bosh-softlayer-cpi-release