freebsd-base.7: Break examples into subsections

Break the examples into subsections, so that we can have multi-step
examples.

MFC after: 3 days (to 15 only)
Discussed with: ivy
Differential Revision: https://reviews.freebsd.org/D55526

(cherry picked from commit 5f922bd20d81af4b5759b8f104d5c22ee3e5cd1b)