[docusaurus] Background visual for website

[jtfirek]

replace the green background with a visual

rough draft idea:

[dawsbot]

Although I like this image, I don't have enough interest to buy it, hire the designer, etc. We should consider if there is a simpler solution which provides just as-much fun. (let's take inspiration from https://gitmoji.dev/)

and perhaps the github logged-out homepage: