Add README with coverage/complexity/duplication badges

Author: tbjers

README.md

@@ -0,0 +1,35 @@
+# example-typescript
+
+[![coverage badge](https://img.shields.io/endpoint?url=https%3A%2F%2Fdemo.coveragetracker.dev%2Fapi%2Fbadge%2FCoverageTracker%2Fexample-typescript%2Fcoverage.json)](https://demo.coveragetracker.dev/CoverageTracker/example-typescript?metric=coverage)
+[![complexity badge](https://img.shields.io/endpoint?url=https%3A%2F%2Fdemo.coveragetracker.dev%2Fapi%2Fbadge%2FCoverageTracker%2Fexample-typescript%2Fcomplexity.json)](https://demo.coveragetracker.dev/CoverageTracker/example-typescript?metric=complexity)
+[![duplication badge](https://img.shields.io/endpoint?url=https%3A%2F%2Fdemo.coveragetracker.dev%2Fapi%2Fbadge%2FCoverageTracker%2Fexample-typescript%2Fduplication.json)](https://demo.coveragetracker.dev/CoverageTracker/example-typescript?metric=duplication)
+
+A small, idiomatic TypeScript invoicing/cart library used as the JS/TS
+reference example for [Coverage Tracker](https://coveragetracker.dev). It
+exists to give the JS/TS row in the
+[coverage report generation guide](https://coveragetracker.dev/docs/generating-coverage-reports)
+a live, working reference, and to populate the
+[demo dashboard](https://demo.coveragetracker.dev) with real trend data.
+
+**This is a demo/marketing repo, not a test suite for Coverage Tracker
+itself.**
+
+## What's here
+
+- `src/` — discount/cart calculations, currency formatting, and validation
+  helpers, each with real branching logic.
+- `test/` — a [vitest](https://vitest.dev) suite with a deliberately
+  uncovered branch or two, so `branch_coverage < line_coverage` shows up on
+  the dashboard.
+- `.github/workflows/coverage.yml` — runs tests with coverage, generates a
+  [Lizard](https://github.com/terryyin/lizard) complexity report and a
+  [jscpd](https://github.com/kucherenko/jscpd) duplication report (a small
+  duplicated block is seeded on purpose), then reports all three to the demo
+  instance via the `coverage-tracker` reporting Action.
+
+## Running locally
+
+```sh
+npm ci
+npm run coverage   # writes coverage/lcov.info
+```