Add information about Early adopter plan (https://gitlab.com/gitlab-org/gitlab-ee/issues/2344 follow-up)
As a follow-up to https://dev.gitlab.org/gitlab/gitlab-ee/merge_requests/515, we should add the information of all features of the Early adopter plan on https://about.gitlab.com/gitlab-com/, as this will be the page which users will be redirected to when clicking on View all Early Adopter features
on the new Billings page (https://gitlab.com/gitlab-org/gitlab-ee/issues/2344).
We should not present the Buy now
button on that case, since Early adopter is not a purchasable plan.