Add support for images in dark mode

[rluvaton]

Images are not displayed properly when dark mode is used, fortunately, GitHub added support for light/dark based images.

It's available by using the prefers-color-scheme in the picture element.

More info here

Light:

Dark:

Images from CONTRIBUTING.md file

[rluvaton]

It looks like the attached image is a mermaid graph (I didn't know GitHub supported it, cool!) so

[marcosmol204]

Opened PR #249