SKILL.md header pointed at same-dir README.md but the pack had no
such file (CHANGELOG was supplied by #217, README was not). This
track adds the README only: purpose, chapter map, appendix
provenance entry point, seeding behaviour, and known boundaries.
It states no rule, changes no SKILL.md semantics, and does not
duplicate the CHANGELOG/script explanations -- overlapping parts
are pointers, with an explicit division-of-labour section.
Deletion retention is written only as the tombstone-design
placeholder, deferring to the skill_seed implementation, because
no tombstone implementation has landed. Test pins that every
file SKILL.md cites as same-directory exists (CHANGELOG, README).
