Clean up the example code in readme

[byCedric]

This change removes the unused imports and should put more focus on the required styling.

[byCedric]

I also noticed the example icons not working great on dark mode. Any objections to adding a white background color to the font example images?

There is an ongoing discussion about darkmode/lightmode versions of markdown in Github here but hasn't lead up to a nice workaround for us yet.

[ccheever]

Seems fine but this is generated by the generateRootReadme function in packages/generator, and so the change should be made there rather than in the README itself or else it will be overwritten the next time the package is generated.