Update nightly badge in README with GH action
[![go report card](https://goreportcard.com/badge/code.cloudfoundry.org/quarks-operator)](https://goreportcard.com/report/code.cloudfoundry.org/quarks-operator)
[![Coveralls github](https://img.shields.io/coveralls/github/cloudfoundry-incubator/cf-operator.svg?style=flat)](https://coveralls.io/github/cloudfoundry-incubator/cf-operator?branch=HEAD)
-| Nightly build | [![nightly](https://ci.flintstone.cf.cloud.ibm.com/api/v1/teams/quarks/pipelines/cf-operator-nightly/badge)](https://ci.flintstone.cf.cloud.ibm.com/teams/quarks/pipelines/cf-operator-nightly) |
+| Nightly build | [![quarks-operator-nightly](https://github.com/cloudfoundry-incubator/quarks-operator/workflows/quarks-operator-nightly/badge.svg)](https://github.com/cloudfoundry-incubator/quarks-operator/actions?query=workflow%3Aquarks-operator-nightly) |
| ------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
<img align="right" width="200" height="39" src="https://github.com/cloudfoundry-incubator/quarks-docs/raw/master/content/en/docs/cf-operator-logo.png">
