chore: add demo link to README.md

[kilianc]

No description provided.

[github-actions]

🔗 Code Coverage Report for go-test-app-01/ at 7e578f0

📔 Total: 70.0%
🎯 Threshold: 66.7%
✅ 70.0% >= 66.7%

Full coverage report

cointoss/main.go:10:	main		75.0%
cointoss/main.go:20:	tossCoin	66.7%
cointoss/main.go:28:	maybe		66.7%
total:			(statements)	70.0%

^{go-beautiful-html-coverage ↗}

[github-actions]

🔗 Code Coverage Report for go-test-app-02/ at 7e578f0

📔 Total: 70.0%

Full coverage report

cointoss/main.go:10:	main		75.0%
cointoss/main.go:20:	tossCoin	66.7%
cointoss/main.go:28:	maybe		66.7%
total:			(statements)	70.0%

^{go-beautiful-html-coverage ↗}