Draft a policy for engaging with comments and users on YouTube

Because virtually all GitLabbers can and should have access to the official GitLab YouTube account and channel, it seems prudent to draft up a policy about engaging with users and videos on the site while logged in.

In short: GitLabbers should ensure that they're logging out of the official GitLab account before engaging with other users on YouTube unless their job responsibilities require that they engage in an official capacity.

cc @sytses