Add possibility to apply Duckduckgo theme via script

[ChrizzDF]

Hi guys, since I'm not allowed to create branches or pull requests,
here my request to update the README.md file.

I think it's nice to provide a possibility to persist the Duckduckgo theme.
I thought about updating the section as follows:

DuckDuckGo
Tokyo Night Theme

• Try out without saving using URL params via this link.
  (by Grafikart)
• Save theme using script to persist by writing Cookies (ported by ChrizzDF)
  1. Visit https://duckduckgo.com/.
  2. Open Browser's Console.
  3. Copy, paste and run the script below.

     var tokyoNight=["9=c0caf5","aa=BB9AF7","7=1a1b26","8=6183BB","j=16161e","x=1abc9c","21=16161E"];
     for(var i=0;i<tokyoNight.length;i++)document.cookie=tokyoNight[i];
     alert('Appearance settings have successfully been updated!');
     location.reload();

I know this approach from the Dracula Theme which I really like,
so I just adapted this script with the Tokyo Night Theme color values.

I also gave the section a bit more structure to make clear that there're different approaches/options to see the theme in Duckduckgo.

I think many people would love to know about this easy way to apply the theme instead of manually porting the colors to Duckduckgo's theme settings.