Fix readme

Author: rcannood

README.md

@@ -1,4 +1,8 @@
-[![](https://openproblems.bio/images/heros/home_hero_text.png)](https://openproblems.bio)
+<picture>
+  <source media="(prefers-color-scheme: dark)" srcset="https://raw.githubusercontent.com/openproblems-bio/logos/refs/heads/main/banner/openproblems-banner_white-1024px.png">
+  <source media="(prefers-color-scheme: light)" srcset="https://raw.githubusercontent.com/openproblems-bio/logos/refs/heads/main/banner/openproblems-banner-1024px.png">
+  <img alt="OpenProblems logo." src="https://raw.githubusercontent.com/openproblems-bio/logos/refs/heads/main/banner/openproblems-banner-1024px.png">
+</picture>
 
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