Update README.md to use higher resolution images

Author: Ocean-OS

README.md

@@ -1,7 +1,7 @@
 <a href="https://svelte.dev">
 	<picture>
-      <source media="(prefers-color-scheme: dark)" srcset="assets/banner_dark.png">
-      <img src="assets/banner.png" alt="Svelte - web development for the rest of us" />
+      <source media="(prefers-color-scheme: dark)" srcset="assets/banner_dark_large.png">
+      <img src="assets/banner_large.png" alt="Svelte - web development for the rest of us" />
   </picture>
 </a>