Add to doc: Comments for Personal Snippets
New feature 
Comments for Personal Snippets - https://docs.gitlab.com/ce/user/snippets.html#snippets
From release post copy: Collaboration often happens in snippets, even personal snippets. With this release, you now have a comment thread for each personal snippet, just like project snippets.
https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/5551/diffs#note_29994940