title: how to promote master, after failover on postgresql with docker
body: <p>first of all i'm using this setup  <a href="https://github.com/paunin/postgres-docker-cluster" rel="noreferrer" title="Docker repositorie with is own docker compose file">postgres-docker-cluster</a>,  everything works fine during the fail-over, i stop the master and the slave1 take its place, but if i turn the master back on im not sure how to promoted to master again, i would appreciated any pointers on the right direction, do i need to manually promote it? sorry i'm pretty new at this concept(ha).
  This docker uses <strong>repmgr</strong>, <strong>pgpool2</strong> and <strong>postgre 9.5</strong>.</p>
  
  <p>some info on the docker</p>
  
  <ul>
  <li><a href="https://hub.docker.com/r/paunin/postgresql-cluster-pgsql/" rel="noreferrer">postgresql-cluster-pgsql</a></li>
  <li><a href="https://hub.docker.com/r/paunin/postgresql-cluster-pgpool/" rel="noreferrer">postgresql-cluster-pgpool</a></li>
  <li><a href="https://github.com/paunin/postgres-docker-cluster/blob/master/docker-compose.yml" rel="noreferrer">docker-compose.yml</a></li>
  </ul>