Update README.md

Create Rustlings Codespace in one click

Author: eroullit

README.md

@@ -66,7 +66,7 @@ If you get a permission denied message, you might have to exclude the directory
 
 [![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/rust-lang/rustlings)
 
-Open up Rustlings in [Codespaces](https://docs.github.com/en/codespaces/developing-in-codespaces/creating-a-codespace-for-a-repository#creating-a-codespace-for-a-repository)
+[![Open Rustlings On Codespaces](https://github.com/codespaces/badge.svg)](https://github.com/codespaces/new/?repo=rust-lang%2Frustlings&ref=master)
 
 ## Manually