Add main-bosh-docker README
Add main-bosh-docker README

[#140873479](https://www.pivotaltracker.com/story/show/140873479)

Signed-off-by: Adrian Zankich <06c4bdd5da019c5d30546d0230d625621ed622b0@pivotal.io>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh