Record README delivery and clarify Dart prerequisite

docs/implementation.md

@@ -132,3 +132,12 @@ in the README. Validation: no tracked root `.vscode` files, ignore rule verified
 and diff whitespace check passed. Runtime tests are unnecessary for this change.
 
 Delivery: [PR #15](https://git.sendico.io/tech/sxchnge/pulls/15), branch `editor-14`.
+
+## Root README refresh
+
+Task [#18](https://git.sendico.io/tech/sxchnge/issues/18), delivered in
+[PR #19](https://git.sendico.io/tech/sxchnge/pulls/19) on `docs-18`, documents
+current packages, app/website commands, verification previews, analytics limits,
+skill location and contribution workflow. Local links and diff checks pass;
+commands and prerequisites were checked against repository configuration.
+Documentation only; no runtime tests were run.