Add buildah

doc/ci/docker/using_docker_build.md

@@ -23,7 +23,7 @@ To enable Docker commands for your CI/CD jobs, you can use:
 - [Docker socket binding](#use-docker-socket-binding)
 
 If you don't want to execute a runner in privileged mode,
-but want to use `docker build`, you can also [use kaniko](using_kaniko.md).
+but want to use `docker build`, you can also use [`kaniko`](using_kaniko.md) or [`buildah`](https://github.com/containers/buildah).
 
 If you are using shared runners on GitLab.com,
 [learn more about how these runners are configured](../runners/index.md).