Feature/29 cent os readme fix

I encountered problems running spinach tests on CentOS. I found out a git version in-compatable with Gitlab tests is the only binary available for centOS. I documented in the Readme my installation setup for CentOS, and also included the Git note on how to get around that by installing from source over the top of existing binary. The git version is Nearly the same so it is very easy to overlook. #29 (closed) https://gitlab.com/gitlab-org/gitlab-development-kit/issues/29

I tried to follow the contributing guidelines from main gitlab the best I could.