fix 1-click button

Author: raphaeltm

samples/rocket/README.md

@@ -1,6 +1,6 @@
 # Rocket
 
-[1-click deploy](https://portal.defang.dev/redirect?url=https%3A%2F%2Fgithub.com%2Fnew%3Ftemplate_name%3Dsample-rocket-template%26template_owner%3DDefangSamples)
+[![1-click-deploy](https://defang.io/deploy-with-defang.png)](https://portal.defang.dev/redirect?url=https%3A%2F%2Fgithub.com%2Fnew%3Ftemplate_name%3Dsample-rocket-template%26template_owner%3DDefangSamples)
 
 This sample demonstrates how to deploy a very simple Rocket app. Rocket is a web framework for Rust.