docs: add light/dark scheme support for star history chart

Author: sisp

README.md

@@ -151,4 +151,10 @@ codebase.
 
 And thanks to all financial supporters and folks that give us a shiny star! ⭐
 
-[![Star History Chart](https://api.star-history.com/svg?repos=copier-org/copier&type=Date)](https://star-history.com/#copier-org/copier&Date)
+<a href="https://star-history.com/#copier-org/copier&Date">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="https://api.star-history.com/svg?repos=copier-org/copier&type=Date&theme=dark" />
+    <source media="(prefers-color-scheme: light)" srcset="https://api.star-history.com/svg?repos=copier-org/copier&type=Date" />
+    <img alt="Star History Chart" src="https://api.star-history.com/svg?repos=copier-org/copier&type=Date" />
+  </picture>
+</a>