UX Guide: Add personas

Added the UX Personas information to the UX Guide.

@sarahod @regisF @victorwu Just moved the persona information to the UX Guide instead of the handbook (as discussed here: https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/4897#note_23383580). Let me know if you have any questions or concerns.

@regisF - If this looks good to you, could you merge it? Thanks!

assigned to @regisF

mentioned in merge request gitlab-com/www-gitlab-com!4897 (closed)

@awhildy why CI Skip?

@regisF When I add documentation to the UX guide in the CE codebase, my understanding from @stanhu was that the CI tests weren't really necessary (are we are just editing MD files), and it saves us resources (and thus $) to not run it every time. Happy to adjust if that is incorrect.

merged

Yes, documentation changes that are compiled (e.g. blog posts on gitlab.com) need CI, but not in this case.