message: fix chart-repo-sync cmd link
  cc
diff: ChartSvc is a service for KubeApps that reads chart metadata from the database
  and presents it in a RESTful API. It should be used with the
  -[chart-repo-sync](https://github.com/kubeapps/chart-repo-sync) to populate chart
  +[chart-repo-sync](https://github.com/kubernetes-helm/monocular/tree/master/src/api/cmd/chart-repo-sync) to populate chart
  metadata in the database.
  