docs: Switch readme logo to logo_large.webp

Author: dbirks

README.md

@@ -1,5 +1,5 @@
 <div align="center">
-    <img src="./media/logo_small.webp" alt="Spec Kit Logo"/>
+    <img src="./media/logo_large.webp" alt="Spec Kit Logo"/>
     <h1>🌱 Spec Kit</h1>
     <h3><em>Build high-quality software faster.</em></h3>
 </div>