Adjust image in README.md for dark mode
Adjust image in README.md for dark mode

Note that for now, due to a bug in GitHub rendering, we also have to add the `#gh-light/dark-mode-only` anchor to the link.

See https://twitter.com/_francislavoie/status/1463752697006411776 .
quarkusio/quarkus,quarkusio/quarkus,quarkusio/quarkus,quarkusio/quarkus,quarkusio/quarkus