docs(readme): add dark mode support to star history chart

Author: ssddOnTop

README.md

@@ -76,4 +76,10 @@ Contributions welcome!
 
 ## Star History
 
-[![Star History Chart](https://api.star-history.com/svg?repos=gpmcp/api-keys-simplified&type=date&legend=top-left)](https://www.star-history.com/#gpmcp/api-keys-simplified&type=date&legend=top-left)
+<a href="https://www.star-history.com/#gpmcp/api-keys-simplified&type=date&legend=top-left">
+ <picture>
+   <source media="(prefers-color-scheme: dark)" srcset="https://api.star-history.com/svg?repos=gpmcp/api-keys-simplified&type=date&theme=dark&legend=top-left" />
+   <source media="(prefers-color-scheme: light)" srcset="https://api.star-history.com/svg?repos=gpmcp/api-keys-simplified&type=date&legend=top-left" />
+   <img alt="Star History Chart" src="https://api.star-history.com/svg?repos=gpmcp/api-keys-simplified&type=date&legend=top-left" />
+ </picture>
+</a>