Update README.md fix banner width (ultralytics#3785)

README.md

@@ -178,11 +178,8 @@ Get started in seconds with our verified environments and integrations, includin
 
 We are super excited about our first-ever Ultralytics YOLOv5 🚀 EXPORT Competition with **$10,000** in cash prizes!  
 
-<div align="center">
-<a href="https://github.com/ultralytics/yolov5/discussions/3213">
-    <img src="https://github.com/ultralytics/yolov5/releases/download/v1.0/banner-export-competition.png"/>
-</a>
-</div>
+<p align="center" href="https://github.com/ultralytics/yolov5/discussions/3213">
+  <img width="850" src="https://github.com/ultralytics/yolov5/releases/download/v1.0/banner-export-competition.png"></p>
 
 
 ## <div align="center">Why YOLOv5</div>