Update README.md with a new theme repo

The repo referenced is currently unmaintained, so I made a fork with some fixes and improvements, with more to come. Maybe a good idea to reference it as well / replace it?

Author: kerichdev

readme.md

@@ -101,7 +101,7 @@ If you get an error "is damaged and can’t be opened." when launching the app,
 
 You can load CSS files to change the look of the application (Options > Visual Tweaks > Themes).
 
-Some predefined themes are available in https://github.com/OceanicSquirrel/themes-for-ytmdesktop-player.
+Some predefined themes are available in https://github.com/kerichdev/themes-for-ytmdesktop-player.
 
 ## Dev