Document BrowserStack demo

Author: aidenjbrown

browserstack-demo/README.md

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+# BrowserStack Playwright Demo
+
+This demo runs a Playwright smoke test against the button click counter training plugin using BrowserStack.
+
+## Local setup
+
+Set BrowserStack credentials in your shell:
+
+```bash
+export BROWSERSTACK_USERNAME="..."
+export BROWSERSTACK_ACCESS_KEY="..."