Update README.md

Author: laurentpf5

README.md

@@ -24,7 +24,7 @@ $ cp Dockerfil.nplus Dockerfile
 ```
 Now to build the frontend-proxy image with NGINX, issue the following: 
 ```shell
-$ docker build -f src/nginx-frontend-proxy/Dockerfile -t latest-frontend-proxy . 
+$ docker build -f src/nginx-frontend-proxy/Dockerfile -t ghcr.io/open-telemetry/demo:latest-frontend-proxy . 
 ```