Define a favicon for google search results

[christophscheuch]

https://developers.google.com/search/docs/appearance/favicon-in-search

Let's also get a nicer icon like the other website :)

[christophscheuch]

So we actually already have that information in the header:

<link href="./images/favicon.png" rel="icon" type="image/png">

I guess we have to wait for the google agent to scrape it.