Add two more demo examples for the avatars component
Once the ~"pajamas::create" phase of the ~"component::avatars" have been completed for the two more component variants described in gitlab-org/gitlab-ui#285 (comment 185788063) and gitlab-org/gitlab-ui#285 (comment 185800599), let's bring back the two remaining variants as demo examples in the usage guidelines section.
Edited by George Tsiolis