adding steps required for build of binary which exist in ci yaml

I was running into the following error on a fresh clone, and trying to build against Go v1.5.4

imports gitlab.com/gitlab-org/gitlab-pages/internal/httputil: use of internal package not allowed

This is alleviated by following the steps I've detailed in the README.md, and are also detailed in the .gitlab-ci.yml for build steps in the before-script.