Add basic tests for website and cheatsheet

- [ ] Maybe [visual regression testing](https://docusaurus.io/blog/upgrading-frontend-dependencies-with-confidence-using-visual-regression-testing). Probably use [applitools](https://applitools.com/) instead
- [ ] An end-to-end web testing framework
- [ ] Docs
- [ ] Homepage
- [ ] Cheatsheet web
- [ ] Cheatsheet local