README: Remove mentions of circleci (#11580)

Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>

Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>

README.md

@@ -7,7 +7,7 @@ examples and guides.</p>
 
 <div align="center">
 
-[![CircleCI](https://circleci.com/gh/prometheus/prometheus/tree/main.svg?style=shield)][circleci]
+[![CI](https://github.com/prometheus/prometheus/actions/workflows/ci.yml/badge.svg)](https://github.com/prometheus/prometheus/actions/workflows/ci.yml)
 [![Docker Repository on Quay](https://quay.io/repository/prometheus/prometheus/status)][quay]
 [![Docker Pulls](https://img.shields.io/docker/pulls/prom/prometheus.svg?maxAge=604800)][hub]
 [![Go Report Card](https://goreportcard.com/badge/github.com/prometheus/prometheus)](https://goreportcard.com/report/github.com/prometheus/prometheus)
@@ -178,7 +178,6 @@ For more information on building, running, and developing on the React-based UI,
 ## More information
 
 * Godoc documentation is available via [pkg.go.dev](https://pkg.go.dev/github.com/prometheus/prometheus). Due to peculiarities of Go Modules, v2.x.y will be displayed as v0.x.y.
-* You will find a CircleCI configuration in [`.circleci/config.yml`](.circleci/config.yml).
 * See the [Community page](https://prometheus.io/community) for how to reach the Prometheus developers and users on various communication channels.
 
 ## Contributing
@@ -190,5 +189,4 @@ Refer to [CONTRIBUTING.md](https://github.com/prometheus/prometheus/blob/main/CO
 Apache License 2.0, see [LICENSE](https://github.com/prometheus/prometheus/blob/main/LICENSE).
 
 [hub]: https://hub.docker.com/r/prom/prometheus/
-[circleci]: https://circleci.com/gh/prometheus/prometheus
 [quay]: https://quay.io/repository/prometheus/prometheus