Add note about support in the GDK.
Add note about support in the GDK.

gitlabhq/gitlab-ci-runner,cui-liqiang/gitlab-ci-runner,gitlabhq/gitlab-ci-runner,andrewmunsell/gitlab-ci-runner,andrewmunsell/gitlab-ci-runner,cui-liqiang/gitlab-ci-runner,mfittko/gitlab-ci-runner,mfittko/gitlab-ci-runner