Merge #11633

11633: Automatically change text color in logo based on dark mode r=Veykril a=arzg

Currently the black text in the logo in the README just has a white stroke so it’s readable in dark mode. This PR adds automatic detection of whether the user is using system dark mode, and if they are changes the text colour to white and removes the stroke.

Before:

<img width="910" alt="Screen Shot 2022-03-06 at 10 54 35 pm" src="https://user-images.githubusercontent.com/31783266/156921920-7ac88aa4-bab6-44c2-be37-30338a2d9ec9.png">

After (now in Chrome because this doesn’t seem to work in Safari):

<img width="822" alt="Screen Shot 2022-03-06 at 11 10 12 pm" src="https://user-images.githubusercontent.com/31783266/156922615-41fe63e0-7901-4cb1-a229-6d37b6e4369a.png">
<img width="820" alt="Screen Shot 2022-03-06 at 11 10 25 pm" src="https://user-images.githubusercontent.com/31783266/156922619-1bdd5b9c-89ac-4fe1-bf17-1a1ac4ead805.png">

Co-authored-by: Luna Razzaghipour <[email protected]>