Add Go Report Card Badge to README

[bupd]

Request

Add the Go Report Card badge to the README to showcase code quality.

[![Go Report Card](https://goreportcard.com/badge/github.com/container-registry/harbor-satellite)](https://goreportcard.com/report/github.com/container-registry/harbor-satellite)

[minhpham1810]

Hi @bupd , I can take this. I’ll add the Go Report Card badge to the README and open a PR shortly.