[3.12] gh-124182: Explain naming rules for struct sequence types (GH-124335) (#125056)

gh-124182: Explain naming rules for struct sequence types (GH-124335)
(cherry picked from commit 3287c834e5370294e310450115290979aac06efa)

Co-authored-by: ffelixg <142172984+ffelixg@users.noreply.github.com>