SEO improvement

There is a few things to do in order to have a better SEO and experience:
- add a [meta description](https://web.dev/meta-description/)
- add a [meta theme-color](https://web.dev/themed-omnibox/)
- add a [custom splash screen](https://web.dev/splash-screen/)
- add an [apple-touch-icon](https://web.dev/apple-touch-icon/)