docs: replace microbadger's image info badge

MicroBadger.com will shutdown on 1st July 2021

Author: buchdag

README.md

@@ -1,6 +1,6 @@
 ![Tests](https://github.com/nginx-proxy/acme-companion/workflows/Tests/badge.svg)
 [![GitHub release](https://img.shields.io/github/release/nginx-proxy/acme-companion.svg)](https://github.com/nginx-proxy/acme-companion/releases)
-[![Image info](https://images.microbadger.com/badges/image/nginxproxy/acme-companion.svg)](https://hub.docker.com/r/nginxproxy/acme-companion "Click to view the image on Docker Hub")
+[![Docker Image Size](https://img.shields.io/docker/image-size/nginxproxy/acme-companion?sort=semver)](https://hub.docker.com/r/nginxproxy/acme-companion "Click to view the image on Docker Hub")
 [![Docker stars](https://img.shields.io/docker/stars/nginxproxy/acme-companion.svg)](https://hub.docker.com/r/nginxproxy/acme-companion "Click to view the image on Docker Hub")
 [![Docker pulls](https://img.shields.io/docker/pulls/nginxproxy/acme-companion.svg)](https://hub.docker.com/r/nginxproxy/acme-companion "Click to view the image on Docker Hub")