docs(readme): describe the OF module, fix the stale test count

README.md said "lib/rites/ contains rite_ef and nothing else" and
"treat any claim of multi-rite support as a design goal rather than a
feature" -- false as of this branch: lib/rites/ also contains rite_of,
wired into a working --rite of. Rewrite the opening paragraph to state
what actually ships, with the OF's own honest limits relative to the
EF's (no published-ordo witness, Polish-vernacular lectionary lineage,
known-wrong pinned dates, First reading + Gospel only).

Also fixes two further stale numbers this same paragraph's neighbours
carried, unrelated to this branch's own content but caught while here:
"dune test # fast suite, 568 tests" (actual: 887) and "## Status"'s
"v0.9.0, EF only. 569 tests" (actual tag: v1.0.0; this line is written
from an unreleased branch, stated as such rather than inventing a
version number).

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