v0.2.5 — A README that no longer calls itself unreleased

A documentation patch. The README carried a section announcing its own release branch:

## Unreleased Nafinity integration candidate

Target branch: `v0.2.4-rc`. This behavior is not a published release yet.

v0.2.4 was tagged from that file, so everyone who installed it read that the version they had
just installed was unreleased. A README ships inside the Composer package, and a tag cannot
move, so reaching existing installations needs this release.

The paragraph underneath it is gone as well. It sat after the License, where the document
ends, and read like release notes in prose: four unrelated internal changes, each only
meaningful to someone who knew the previous behaviour. Those facts are in the
v0.2.4 notes, where a reader looks
for what changed, and the behaviour they describe is unchanged here.

No code changes. Runtime behaviour, public APIs and dependency constraints are identical
to v0.2.4.

Validation: the tagged commit passed CI, and its tree passed the suite with 137 tests and
280 assertions.