docs(changes): Note doc-pytest-plugin directive in sphinx-autodoc-pytest-fixtures

why: The CHANGES workspace package entry for sphinx-autodoc-pytest-fixtures
only described the initial release; the new doc-pytest-plugin directive
shipped on this branch needs a release note.
what:
- Add doc-pytest-plugin summary to sphinx-autodoc-pytest-fixtures entry

Author: tony

CHANGES

@@ -34,6 +34,11 @@ $ uv add gp-sphinx --prerelease allow
   badges, classified dependency lists, reverse-dep tracking, and auto-generated
   usage snippets. Frozen dataclasses for pickle-safe incremental builds, parallel-safe,
   WCAG AA badge contrast, and pytest 9+ compatible.
+  New: `doc-pytest-plugin` directive generates a standard pytest plugin page
+  (install block, `pytest11` autodiscovery note, fixture summary and reference)
+  from a single directive call. Optional `:project:`, `:summary:`, `:tests-url:`,
+  and `:install-command:` options; body is free-form. Use `autofixture-index` +
+  `autofixtures` directly when custom layout is needed.
 - `sphinx-fonts` — Self-hosted web fonts via Fontsource CDN. Downloads at build time,
   caches locally, and injects `@font-face` CSS with preload hints and fallback
   font-metric overrides for zero-CLS loading.