examples: add direct link to Dockerfile (#58793)

examples/with-docker/README.md

@@ -24,7 +24,7 @@ You can view your images created with `docker images`.
 
 ### In existing projects
 
-To add support for Docker to an existing project, just copy the `Dockerfile` into the root of the project and add the following to the `next.config.js` file:
+To add support for Docker to an existing project, just copy the [`Dockerfile`](https://github.com/vercel/next.js/blob/canary/examples/with-docker/Dockerfile) into the root of the project and add the following to the `next.config.js` file:
 
 ```js
 // next.config.js