Follow-up from "Release post - GitLab 11.5" - missed deliverable

The following discussion from gitlab-com/www-gitlab-com!16021 (merged) should be addressed:

• @bikebilly started a discussion: (+11 comments)

  @akaemmerle required field documentation_link is missing for this item!

This is about the "Activity dashboard redesign" and the fact that we don't have any docs about the activity dashboard.