Update README Brand mark

[AnthonyRollins]

@thekaveman I use the white background theme for Github, and our brandmark doesn't look the same as the white is hidden in different themes. We will need to create a brand mark that doesn't have white or black to be visible in any Github theme. My initial thoughts, but curious what you think we can do.

See screenshot:

[thekaveman]

@AnthonyRollins thanks for the heads up, yeah I think we just have to remove it for now. Since our website is a dark background and so is my GitHub theme I didn't even think about this 😆

I'm not sure if we can target a light/dark theme with a different image but could look into that.

[thekaveman]

Huzzah!

https://github.blog/changelog/2022-05-19-specify-theme-context-for-images-in-markdown-beta/

https://github.blog/changelog/2022-08-15-specify-theme-context-for-images-in-markdown-ga/

So now we just need a light/dark mode version of the pattern and it will work like so: