Create a light version of the project icon

[bengreenier]

Is your feature request related to a problem? Please describe.

Based on discussion in #135 - When viewing the readme in GitHub dark mode the contrast on the logo is a bit rough. This issue tracks creating a lighter version of the logo for use in cases like that.

Describe the solution you'd like

A light version of https://github.com/RainwayApp/bebop/blob/master/assets/128%402x.png

Describe alternatives you've considered

Leaving as is. Since this is a cosmetic-only change, it's pretty low priority and I don't see an alternative other than not doing it.

[bengreenier]

If we're able to provide a lighter icon, we should also update the readme to use https://github.blog/changelog/2021-11-24-specify-theme-context-for-images-in-markdown/ to conditionally display the color-correct version of the logo.