Minor aesthetic update for Markdown files

[mahozad]

GitHub recently made it possible to Specify theme context for images in Markdown.

Do you think it would be better to provide separate dark/light version of the Wasm logo and use them in Markdown files like CG-01-04.md?

I can provide a pull request if you'd like.

Logo for light theme	Logo for dark theme

[dtig]

I don't have a particular preference here, if anyone else does please respond on this thread. If there is sufficient interest, a PR would be welcome.