Add readme's for the doc.gitlab.com site.
 Merge branch 'add-readme-for-doc-site' into 'master'

Add-readme-for-doc-site
Correct extension of readme in doc dir.
 Merge branch 'readme-is-md' into 'master'

Readme-is-md
Link to the documentation site.
 Merge branch 'link-to-doc-site' into 'master'

Link-to-doc-site
Merge branch 'master' of github.com:gitlabhq/gitlab-ci